it has to do with people having this deluded thinking that vanilla was so great because of the amount of skill it took when it had nothing to do with why vanilla was so fun
Vanilla was "artificially" tough because the correct gear wasn't hurled at everyone from the start. If you pulled a 2-3 mobs a few levels higher than you it was an actual threat... People didn't know the correct pathing through zones, you'd run into areas which would destroy you. You'd try shit you know your character wasn't geared for whilst learning to kite/cc etc to make it work because it was an actual challenge and you couldn't be arsed running back in a couple of levels.
Ofc vanilla now looks simple, no-one who has spent years on this game and now has 80+ optimised keybinds/macro's is going to struggle with anything vanilla throws at them yet there's some nostalgia value and it's pretty chill for solo play. The main point though is it's a hell of a lot more entertaining than the joke that is live solo play.