Why have alternative builds all died down?

I can't be the only one who feels like champions are getting all these unique new mechanics (new champs or reworks), yet it makes them so one-dimensional on doing "that one thing", that different play styles are being lost more and more.

I do miss being able to build AP or AD or champs who didn't use those as their primary stats, since they usually gave the champ a completely new play style and were more often than not "fun" off-meta picks.

Who remembers AP Tristana, which changed Tristana's late game, long range, hyper carry play style to lane bully/all in "one shot" champ? AD Malzahar, which moved all his reliance on his E onto voidlings and made him play around those? Old AP Sion, which made him bursty/shieldy compared to his AD playstyle which was a late game scaling healing menace? Old AP Xin, which made him less reliant on bursting someone down with his old knockup and Q, and more reliant on healing?

Those are the top examples which come to mind, but it's not just taking away the "AP on AD champ and vice versa" play style. New runes, item builds (especially AP!) all provide very little diversity, or at least less diversity than before they were turned into this.

I'm not saying some "diverse" builds weren't oppressive in the past and they deserve to be removed (or at least tuned... but we got the former) - from tank assassins (Ekko, Fizz, old Akali) to some legends like AP Yi (purposely not mentioned above, because this one is a good example of a build which was objectively bad to have in the game)

I know this might be a pointless rant because this game hasn't been oriented around promoting off-meta and diversity for a long time now, and these changes have been happening since long ago (most of the ones mentioned here have happened awhile ago), though as someone who used to enjoy playing off-meta, I can't help but wonder where this game is heading to and whether just about every different play style will become extinct or not change the champ's play style as much as it should.