"Never attribute to malice that which is adequately explained by stupidity."

The simplest explanation is an out-of-touch billionaire who got rich off other people's ideas and spent his life surrounded by yes-men had an idea that he could reverse the course of a declining social media corporation. He boasted about this, and apparently even convinced himself, enough to make a half-hearted (yet legally binding) offer. He then learned he would lose billions if he backed out of the deal.

Those are the facts. The rest is a fine conspiracy theory, but there's just no clear, provable evidence. He hasn't personally benefited in an obvious way, either before the sale, or since. No one can prove the Saudis, Koch Brothers, Trump, or anyone else put him up to it.

Though I'm totally willing to hear evidence I might have missed...

Because it wasn't he's just bad at business

Twitter is too egalitarian for him and his financiers. And tweaking. ThE AgOrIThM for political gain was too much temptation for his financiers.

Mastodon was just the spanner that could be the downfall of their Evil Plan. Zuck tried to detail Mastodon with Threads, but that is going nowhere too, especially in the EU.