At least in my own bubble, many did switch to Mastodon. Those that didn't are looking at other options, because the whole federation idea and things like home instances didn't appeal to them or were simply too complicated (they want a service that at least hides its decentralized nature).
Because it doesn't come with instructions and there's a lot of "buts". For example, it took me a while to understand that, for example, I can't log in "Mastodon.world" with my "Mastodon.social" account, I had to go to "Mastodon.social" to log in and THEN I can access to the content in "Mastodon.social". Also, there's the problem of instances blocking other instances. I would be pretty salty if I couldn't access an account I followed, because the admins of the instance in which the account is hosted, decided to block the instance in which my account is in. That's why the mayority of users go to the biggest instance (Lemmy.world and Mastodon.social for example), because instances blocking the biggest instance is unlikely to happen (you would block a lot of potencial users and therefore, diminished attractiveness of your instance). But everyone doing that defeats the whole point of federalization. Also, there's the problem of defederalizing of instances. Also, the problem of safety, privacy and security. For example, a massive security fault was recently discovered in Mastodon and a server was raised by the police and all of it's data captured by the police. In simple words, the fediverse is not the panacea it was sold like, the kinks are not ironed out.
And what is when X decides to ban an account you are interested in? You can't do anything against it. In your mastodon you could still read it on that instance. Or maybe there is a client where you can add two accounts and show content of both? And do you think X or Bluesky does not cooperate with law enforcement and gives data if the US government wants it?
So... what if a news article links to a toot or Lemmy post? They're most likely to link to the instance that the post was submitted from, and most people aren't going to understand that they have to go search for the post from their home instance if they want to like, vote, reply, or retoot. Email made sense to people because it is basically all direct messaging, but public linking from articles and such is going to be difficult.
There are a ton of reasons not to like it and they're evident on Lemmy pretty notably, let alone other platforms. The entire idea of being able to defederate and federate at will is a big feature of these platforms but they're also the part that people like the least. If the server you're on defederates from another server you like, you have no choice but to start all the way from the beginning if you need to choose another instance to join. At the same time, each instance gets its own version of every single community. If you join an instance that federates with lots of other instances, you're very likely to see the exact same posts multiple times since each community is completely unique and separate (again, a feature for some, a boon for others).
Federation is great for a few reasons and really horrible for others. It's not the single answer that works for everyone.
Yeah, if you don't like it just create and account on a generic big one that let's you access most content and just go with it. Act as if centralized. People like to create problems for no reason. If other people care about choice and the tech behind it and the new possibilities allowed, let them be happy for it.
It's literally like email. Most people just have a gmail one and that's most common. Others care about specific services, prices, choice, privacy features, etc, and the trch allows people to make that choice without compromising the primary purpose which is connecting people.
Everyone should have a federated account just like everyone has a email account for most things that require it. More and more places are starting to have proper integration for example commenting on blogs instead of the other stupid common alternative (discourse or wtv is the name I don't remember).
From an average outsider perspective is hard to know what is "the big one" in a federated system. And i think links online are what break federated systems. If you get linked to some content from another instance than your own. Then you've got do deal with the url bar yourself in a specific way that is never well documented (only passed around via word of mouth) so you can log in and interact with said content. A baked in "instance switch" at the top of such services that would redirect you to the same content on another instance would be the best solution but I've not seen anything like that yet.
There are browser extensions that make sure any link opens in the user home instance. And I think there were recent improvements recently to improve the UX in those cases.
There's always the true known universal way which is get the url and past it in the search box of the home instance. If installing a browser extension is too much for most users.
It's obvious we are not at peak perfect UX, and work needs to be done and will be done eventually, but it's not having to learn 2 or 3 new things that should be seen as a blocker to using it. Facebook and twitter were very intuitive at some point when nobody knew how things worked. It's all about learning how to work with it.
One thing genuinely confusing is having people reply to a comment I made from a federated instance, and when I try to reply to their comment, I get taken to the reply in the context of the lemmy instance they commented in, not the one I commented in. For example, if I'm on Beehaw and someone from lemmy.ca replies to my comment, and I want to respond to them, what I'll typically do is click on the button below the comment that shows the context of the conversation, because I comment a lot and don't always know what comment I made that someone is replying to. When I do that, it takes me to lemmy.ca, which I can't reply from, because I'm not on lemmy.ca. This is confusing, because this routine thing pulls you into other parts of the fediverse that your reply might exist in, and which other people can see, but you can't comment on that instance because you don't have an account there. But if you go back to your own instance and find your comment through your profile, you can navigate to a reply someone from another instance made and reply to them as long as you're still on your instance. This is both cumbersome and, to a new user, terribly disorienting.