They are also the main developers of the Mastodon software. It is not just hosting the service. The software needs to be able to compete with Bluesky and right now it quite simply does not. The only way to get the quality needed is to have some full time lead developers. Also they need some proper admins to run the websites. Mastodon social is at 250,000 active users right now, but it is also fairly likely to grow fast with what Elon is up to with Twitter. Just to compare Twitter used to have 7500 employees, with a 1000 today.

There are ways around it, like link shorteners and so forth, but the main point is that Meta is afraid.