I see no basis whatsoever for thinking that Jesus's answer to the question about the timing of the destruction of the temple buildings would only be recorded in Luke 21 and not in Matthew 24 or Mark 13. So far, I have never seen you or anyone else give any kind of reasonable explanation for that.
Maybe your idea of reasonable is not the same as someone else's idea of reasonable, thus you reject anything and everything someone else submits because it doesn't live up to your standards as to what qualifies as reasonable? IMO, the following qualifies as reasonable, yet mark my words, you will try and find an unreasonable way around it instead, then insist it had to be rejected since it is not reasonable. IOW, it must be rejected since it causes a conflict with your doctrinal bias concerning some of these things. Unfortunately though, the following ended up lengthier than I was wanting it to be.
Yet there is Luke 17 to consider and factor in here.
Take note that not one thing recorded in Luke 17 below can also be found recorded in Luke 21 but can be found recorded in Matthew 24.
Luke 17:26 And as it was in the days of Noe, so shall it be also in the days of the Son of man.
27 They did eat, they drank, they married wives, they were given in marriage, until the day that Noe entered into the ark, and the flood came, and destroyed them all.
28 Likewise also as it was in the days of Lot; they did eat, they drank, they bought, they sold, they planted, they builded;
29 But the same day that Lot went out of Sodom it rained fire and brimstone from heaven, and destroyed them all.
30 Even thus shall it be in the day when the Son of man is revealed.
31 In that day, he which shall be upon the housetop, and his stuff in the house, let him not come down to take it away: and he that is in the field, let him likewise not return back.
32 Remember Lot's wife.
33 Whosoever shall seek to save his life shall lose it; and whosoever shall lose his life shall preserve it.
34 I tell you, in that night there shall be two men in one bed; the one shall be taken, and the other shall be left.
35 Two women shall be grinding together; the one shall be taken, and the other left.
36 Two men shall be in the field; the one shall be taken, and the other left.
37 And they answered and said unto him, Where, Lord? And he said unto them, Wheresoever the body is, thither will the eagles be gathered together.
Granted, the following can also be found recorded in Luke 21 but none of the above can.
Luke 17:23 And they shall say to you, See here; or, see there: go not after them, nor follow them.
I can see that pertaining to the following.
Luke 21:8 And he said, Take heed that ye be not deceived: for many shall come in my name, saying, I am Christ; and the time draweth near: go ye not therefore after them.
I want to mainly focus on the following part in order for you to explain how that can fit a literal event such as 70 AD?
Luke 17:31 In that day, he which shall be upon the housetop, and his stuff in the house, let him not come down to take it away: and he that is in the field, let him likewise not return back.
32 Remember Lot's wife.
33 Whosoever shall seek to save his life shall lose it; and whosoever shall lose his life shall preserve it.
Compared with...
Matthew 24:15 When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand: )
16 Then let them which be in Judaea flee into the mountains:
17 Let him which is on the housetop not come down to take any thing out of his house:
18 Neither let him which is in the field return back to take his clothes.
You're not going to propose something unreasonable, are you? Thus cherry pick. That Luke 17:31 is not referring to the same era of time, the same events, as Matthew 24:17-18 is referring to, but in regards to Luke 17:26-27 though, it OTOH is referring to the same era of time, the same events as something in Matthew 24 is, meaning this---Matthew 24:37-39?
Let's break it down like such.
-----------------------
A) Luke 17:24 For as the lightning, that lighteneth out of the one part under heaven, shineth unto the other part under heaven; so shall also the Son of man be in his day.
A1) Matthew 24:27 For as the lightning cometh out of the east, and shineth even unto the west; so shall also the coming of the Son of man be.
-----------------------------------
Per your view, is A) and A1) referring to the same thing?
-----------------------------------------------------
B) Luke 17:26 And as it was in the days of Noe, so shall it be also in the days of the Son of man.
27 They did eat, they drank, they married wives, they were given in marriage, until the day that Noe entered into the ark, and the flood came, and destroyed them all.
B1) Matthew 24:37 But as the days of Noe were, so shall also the coming of the Son of man be.
38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark,
39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.
Per your view, is B) and B1) referring to the same thing?
---------------------------------------------------
C) Luke 17:31 In that day, he which shall be upon the housetop, and his stuff in the house, let him not come down to take it away: and he that is in the field, let him likewise not return back.
C1) Matthew 24:17 Let him which is on the housetop not come down to take any thing out of his house:
18 Neither let him which is in the field return back to take his clothes.
Per your view, is C) and C1) referring to the same thing?
-----------------------------------------------
D) Luke 17:34 I tell you, in that night there shall be two men in one bed; the one shall be taken, and the other shall be left.
35 Two women shall be grinding together; the one shall be taken, and the other left.
36 Two men shall be in the field; the one shall be taken, and the other left.
D1) Matthew 24:40 Then shall two be in the field; the one shall be taken, and the other left.
41 Two women shall be grinding at the mill; the one shall be taken, and the other left
Per your view, is D) and D1) referring to the same thing?
-------------------------------------------------
E) Luke 17:37 And they answered and said unto him, Where, Lord? And he said unto them, Wheresoever the body is, thither will the eagles be gathered together.
E1) Matthew 24:28 For wheresoever the carcase is, there will the eagles be gathered together.
Per your view, is E) and E1) referring to the same thing?
-----------------------------------------------------
Obviously, unless you are purposely being dishonest, you can't have, say 4 of these things referring to the same events but one of them not. Therefore, if you are being honest, thus resisting doctrinal bias, you are not going to conclude 4 of these things are referring to the same events but one of them is not. You're going to conclude all 5 of them are referring to the same events, meaning A) and A1) are referring to the same events in both accounts, etc.
Which then presents a major problem with your position since you would be applying Luke 17:30-33 to that of a literal event involving 70 AD. When anyone that has any discernment at all knows that Luke 17:33 couldn't possibly fit 70 AD, a literal event involving literally fleeing from one location to another. Is that how you interpret Luke 17:30-33, in the literal sense, that it is involving literally fleeing from one location to another, such as fleeing to literal mountains? If no, there you go then. Your literal 70 AD interpretation has been debunked and you helped debunk it by agreeing that Luke 17:30-33 is not to be understood in that sense.
There's only one way around this if you don't want to come across as dishonest by insisting that those 5 things recorded in both Luke 17 and Matthew 24, A) A1), B) B1), etc, that only 4 of them are referring to the same thing in both accounts, 1 of them isn't. You have to admit you are wrong about what Matthew 24:15-21 is involving since Luke 17:30-33 can't possibly fit literal events such as 70 AD.