Another issue is that if you choose the wrong node and they decide to shut down for some reason, you lose all your content.[1] There has already been precedent for this.[2] All it takes is being out of the loop for too long and missing a message announcing a shutdown/migration to lose your data. In practice this makes the largest nodes the most appealing for registering an account since their popularity gives you the highest chance of your data living on, which defeats the point of decentralization.
Also, if you're Twitter, you can afford lawyers and moderators to clean up illicit content. If you're operating a Mastodon instance, that responsibility falls on you. It's simply a question of who has more capital, human resources, and free time.[3]
Twitter being centralized means that it's unlikely that Twitter will go away in the long term. That's what would make me choose Twitter over a Mastodon instance if I wanted a public archive of something. I have to wonder what would happen if content of more and more importance started to be hosted on the Fediverse if it was subject to link rot from the nature of federalization.
[1] https://github.com/mastodon/mastodon/issues/10305