Earlier quoted context omitted.
I suspect the initial decision was something like "hey I could actually just buy Twitter, that would be funny". It's less clear to me why he almost immediately started trying to back out. It's probably a waste of a significant chunk of money, but is that all?
It makes more sense if you assume that Elon Musk is both a sometimes successful businessman and also suffering from unmanaged bipolar disorder.
I'm just saying what if... gasp... he simply did something foolish? The blame-it-on-the-bipolar out reinforces the narrative of an infallible person who only make mistakes because of a medical condition. Take that line of thinking one step further and you are now fully onboard the bipolar stigma train.