This isn't really true. There isn't another platform offering what Twitter offers, each platform is different and offers different strengths and weaknesses. While you might theoretically be able to do the same sort of thing on Facebook, say, in practice it just doesn't work well if you try and do the same thing with it.
But this is key, and it works both to drive growth and drive collapse. A major part of what makes Twitter appealing is the people who are on there, if Elon's changes produce the expected degradation in the quality of the platform, a significant number of people will leave. When those people leave the value of the platform to a proportion of the remaining people will drop below their personal thresholds to continue with Twitter and they'll leave, and so on. This can easily snowball into a collapse of the platform and with Twitter already struggling to make money pre-Musk and Musk's incompetence having driven a lot of advertising away that will lead to major losses for the platform. I can see Twitter going from a major platform, regularly cited in News Articles, to a minor interest in a short space of time.
We shall see.