Yeah, I think it's clear that laziness/convenience is the answer.
You're absolutely right about people needing backups -- but ofc selfhosting is too huge a hurdle to expect most folks to embark on.
I wonder what can be done to make the "better" options easier. Can this even be done by the private sector alone given the incentives of capitalism? I'm unsure.
Given how many things we've seen happen in the social media space back-to-back (Elon taking over Twitter, Meta pandering to the new US governing party, TikTok's ban), I can't imagine these events will slow down. That at least fills me with hope that more people will wonder "does it have to be this way?" ...obviously that won't be enough for true mass adoption, but it's a start