I'm sure that is a factor - but the thing with Twitter that insulates it a bit from general "social media audience moving on" like MySpace, etc. - is how institutionalized it became and as quickly as it did. I mean, people focus on the one-off chattering and how "toxic" it all is, because it didn't take a genius to figure out that pithy short tweets were ever conducive to a meaningful platform for discussion.
That said, the backbone of the entire thing is that every large company, most world governments, etc. use it to disseminate information. Heck, a good half of stories on traditional media these days is sourced or begins with something that was tweeted.
The celebrities (and celebrity wannabes) moved to Instagram and TikTok already, and now we are seeing major companies testing the waters if they can do without it. But it has nothing to do with this one tweet in particular, or even Musk in general, it's because they all hate social media and the fact that for the past decade or so corporations have thought they lived or died based on whatever people were saying about them on Twitter or Facebook (even though the majority of the people screaming or praising weren't actually their customers to begin with).
It's such a double-edged sword for them to balance, and lately there have been a few very obvious public examples (and countless smaller ones) that show that what is said on social media does not actually affect real life in the way that these companies (and Wall Street) thought. Just because something is praised by people on social media, doesn't mean the public actually wants to consume it. Just because something is vilified on social media, doesn't mean people aren't going to go out and buy it. And at the end of the day, that's all these companies really care about - what makes them the most money - not about social causes or whatever the think is going to make people online say nice things about them.
What we are really seeing here is companies pulling away from social media, period, even if they are doing it kicking and screaming by focusing more on the "of the moment" one, like TikTok (and all those social media executives want their jobs to exist as long as possible, so they haven't given up, yet).
What will be interesting is what governments do. They don't really have other options to get out statements and other information so quickly and to basically everyone at once. They aren't going to go back to the dark ages of just releasing things to AP/Reuters, but there is no other social platform where they can release something with a click and reach all the people that need to see it (basically the entire mass media) as well as available directly to the public.