Mastodon and federated systems like it will not succeed beyond a tiny niche, will not replace twitter, and don't even solve most of the problems they try to solve. They don't fix the upstream issues that lead to centralization. Incentives mean most users end up centralized on a handful of servers with a worse experience. It's the worst of both worlds. As designed the UX is bad and cannot be fixed because of these iss…
The idea is that the blockchain is a shared, decentralized database and you store simple messages on the blockchain and larger files on something like ipfs. This forms a social graph that a frontend ui can then import and provide a view into (a lens if you will).
It's nice because users just need one account (a wallet) and they have access to the whole social graph if they want, or they can configure their apps to only show certain things. The downside is that it's all public and once you lose your keys you're locked out of your account. Also, you can't really prevent anyone from posting things but you can choose which types of posts you allow on your feed.
It's a different set of tradeoffs that's interesting to explore.