[grumpymouse]

I think things like being able to contact anyone are important to people, but decentralisation doesn't necessarily provide that (e.g. if I sign up on a Mastodon instance will I be able to see the messages of everyone on every Mastodon instance, and will they be able to see mine? Will I even know if somebody I care about can see my messages or not?)

I think decentralisation is not a selling point to most people. It's an implementation detail that they're happy to go along with but it's a negative if it make the experience worse, makes everything more complicated, if they can't talk to the people they know IRL, etc.