Because they have to be stupid. Otherwise the "AUTHORITY" will come knocking. You are too smart, tone back, you have to look like stupid... per the invisible/unspoken rules.
World is fucked. And those who create these invisible rules must be carpet nuclear bombed out of this world.
I don't follow what you are alluding to, if it's content moderation you are reaching to I'd say that has absolutely nothing to do with how unresponsive the UI is, content moderation is not done client-side.
The UI feels janky and laggy, the Messenger itself has noticeable delays, loading new sections is palpably slow.
I cannot understand how, it's not an absurdly complex SPA doing a lot of computation on client-side, it just loads different modals and views.
On the other hand, a complex app doing loads on the client like Onshape, a CAD modeling webapp is very snappy, and satisfying to use.
I don't get how Meta's webapps can be this intensely heavy, even if heavily unoptimised.