Ironically, T-Pain, arguably the poster child of using auto-tune, has a great singing voice[0]. Apparently he used it on purpose to stand out.

Probably explains why it works much better for him than for others: he used it as an instrument, not as a crutch to hide a lack of singing skills.

[0] https://www.youtube.com/watch?v=91ck0vJBygo

I think 80s music is still popular because it is good. Many artists of that era like Elton John, Paul McCartney and specially Stevie Wonder had a very good musical background and the advances in electronic music tech gave them tools to explode their talent to new levels.

This is probably survivorship bias or familiarity bias more than anything.

Music from the 80s/90s that is popular today has stood the test of time; there's a lot more music from these decades that we don't hear today & is not popular. We've also heard those songs a lot more times than contemporary music.