Doesn't this defeat the purpose of decentralisation and the fediverse?
Now, you've just moved everyone to hosted Mastodon, and why not make it even easier - instead of hosting multiple mastodons, just make one single mastodon everyone signs up to... and we've just reinvented Twitter.
Yes, exactly. Every decentralized service eventually backend dominated by a small number of service access providers who are actually willing to deal with hardware.
*eventually becomes
And even the self hosted instances are mostly in a couple of ISPs. (OVH; Hetzner; …).
It is one of the reasons I appreciate masto.host as the owner has made it clear that signups are gated in part by how much of the fediverse it collectively hosts, because they don't want to be a central point of failure, they do want to encourage competition, and they also don't want the headaches of running that big of an instance population.