I think it's a UX problem, which is ultimately an engineering problem. We'll solve it. The issue lies with making decentralized tech work well enough for normie mode. A lot of trade offs and new ways of doing things without a backend need to be designed and built. It's not easy.
I mean obviously there are a lot of "chicken and egg" issues, and I'm loathe to say "oh no the apps are all 'good enough' " --- but people are staying on XMeta not because those UX's are good. In fact, in many instances, they're crap UX. And the users know it.
Ditto is already a way better app than Instagram... cleaner UI, more responsive, easier to navigate, etc.
They're staying there because of network effects.