It is not given to all, because not all are willing to receive it, that's all. It is not the kind of gift that can be forced on someone against their will. The door is open to "whosoever will". A humble and contrite heart He will not turn away. God is not a respecter of persons, and He doesn't violate His own righteousness as to force Himself on anyone. Even the church is admonished not to exercise authority (force) on anyone like the world does. We need to understand the spiritual language of scripture in spirit, because it is spiritual language speaking in spirit.
Its not given to all because all arent Christs/abrahams Seed
Salvation is given only to a seed,not all mankind, Rom 4:16
Therefore it is of faith, that it might be by grace;
to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
He came for the help of the seed of abraham, not all mankind Heb 2:16
16 For verily he took not on him the nature of angels;
but he took on him the seed of Abraham.
For indeed He does not give aid to angels, but He does give aid to the seed of Abraham. NKJV