For me it's the less emphasis on end game, and more enjoyable experience for the entirety of the leveling experience from 1-60. The end game at 60 is just a bonus to me.
Modern WoW puts so much emphasis on end game content, that you blast through 110 levels of just nothing.
I also don't think anyone realistically thinks that classic wow is *better* than the current WoW.
I certainly do not think classic wow is better, there's so much quality of life changes and a lot of fun better things today.
That however, does not mean that classic wow isn't still Fun to play.
I think people confuse "better" with just the fact that classic wow is just as fun as current wow, and we just want to be able to play it again.
Just like picking up old video games to play again, which I am sure many of you have done before.