Any hardware gains and more are used up by stuffing in additional telemetry, ad/engagement scripts, and animations. Devs have grown up on "unused RAM is wasted RAM," work on the latest high-spec Macs, and get incentivized by higher-ups demanding things be ever "modernized" and not to waste time on optimization, which they see as annoying nerd stuff. But even that doesn't explain everything I guess, because I still see a lot of these things in open source projects.