There are some solid reasons given in answer to your question here in the replies and I agree with many of them.

I'll add mine: People have been conditioned to go through a lengthy onboarding process which gathers up tons of personal data. I think this process fools people into believing there is some level of "credibility" involved when there isn't. It's just a personal information vaccuum.

Contrast with nostr onboarding which is done in a fraction of the time (spinning up a Nsec/Npub pair) and I can see how conditioned people could be fooled into believing that "it's not safe" of something or another.

Then, as has been said here, they actually have to deliver quality content to get eyeballs and when they discover that that is difficult (maybe they did at one point on Twitter but then began to rely solely on the algos) they just go back to what's easier. Water always takes the path of least resistance. Delivering quality content is so difficult. I'm getting somewhat better but that battle will be a forever battle.