Why? I ask as someone who doesn't have an X, but am also ignorant to why someone would not use it.
Essentially, almost entirely one-sided coverage of two highly-influential people of contemporary times have warped some people's opinions of them into an irrational and often incoherent rage, leading to boycotts/"cancelling", etc.
In both cases, these were people who were widely-admired - in Musk's case among the same demographic now hates him - when the MSM supported them prior, which then 180°'d when the MSM machine turned against them, for whatever reason.
It's an interesting phenomenon to observe, but is also rather sad as it divides people quite nastily. My response here will likely be downvoted, flagged and receive endless repeats of the media misrepresentstions against both characters.
Criticism will likely be almost entirely devoid of balance, and especially absent of rational acknowledgement that eg, in the orange mans case, hundreds of millions of people love him enough to believe he will lead their country to prosperity.
Unfortunately, such division leads only to a bleak future for all involved, which is why I try here - humbly - to bring some light, and rationality to it, no doubt failing due to the nature of the problem and its effect on people.
X seems like a pretty much the same platform before and since Musk, only since Musk there is noticably-less "curation", and so discussion is more organic, so, some may find it more raw. I like it better, but it's not particularly different really.