I think it was the switch from desktop search traffic being dominant to mobile traffic being dominant, that switch happened around the end of 2016.

Google used to prioritise big comprehensive articles on subjects for desktop users but mobile users just wanted quick answers, so that's what google prioritised as they became the biggest users.

But also, per your point, I think those smaller simpler less comprehensive posts are easier to fake/spam than the larger more compreshensible posts that came before.