Melee's been a shambling corpse for literally close to a decade
like I'm pretty sure the issue here is that streamers and TOs and etc. want their efforts to actually go somewhere and to develop something that's actually accessible to people and is worthwhile for Nintendo and/or other sponsors to actually take notice of
I'm honestly suspicious that the "legality" of PM is just a front, and they're just dropping it left and right because it's not accessible - the only reason they haven't followed suit with Melee is because they're testing the waters to see how viable it is to just move onto Smash 4 (and any subsequent games) so as to minimize the backlash from the Melee community, which I maintain is significantly smaller than it might seem despite it's enormous volume