That's because sinlessness is the standard. Have you not read Rom. 10:4 and the plethora of other NT passages in the epistles that teach a Christian is obligated to follow Christ's example, take on the mind of Christ, or allow Christ to relive His earthly life through them? Why do you think those passages say such things if Christians weren't supposed to focus on being sinless? Christianity is not another false religion where people are only required to feel good about themselves. If t hat's the kind of religion what you want, Hinduism does the job pretty well.
I'm pretty sure you don't realize how ironic your words are. While you speak about people misinterpreting scripture, you imply a Christian isn't supposed to strive towards moral perfection. The obligation to strive towards moral perfection is taught throughout the OT and NT. Literally nobody added that doctrine or made it up because Gen. 1:26-27 explicitly shows human beings were made to acquire God's character. I could also post a multitude of OT and NT verses where God Himself tells someone to be blameless in His sight, a person asked God to help them be blameless in His sight, or an apostle told a Christian audience that God requires them to be blameless to concretely prove this doctrine is taught throughout the Bible.
Christ Himself stated in Matt 5:48 that moral perfection is a standard His followers are supposed to strive towards. That statement is not going to stop being true because people would rather practice a religion that only requires them to feel good about themselves. Christ said the way to eternal life is difficult and that few would find it for a reason.
This is almost good except you are not describing a walk that is by grace. There is no striving against sin unless one is striving to enter INTO Christ where there is no sin.
When we put on Christ we put on His perfection. Otherwise, we are still walking in our own strength.