The oligarchs would be happier being in strict control over a US that barely functioned than they are being insanely wealthy in a wealthy country with a functioning government. That's all.

Rich people just really fucking hate the fact that the general public get to tell them "No" sometimes. They feel they are above us.

A US with no external friends is perfectly fine for them.

Industrialists were pretty happy and supportive of the Third Reich for similar reasons. Better to be on top of a mud pile than near the top of a golden pyramid.

This isn't novel, it's literally how Russia has been for decades now. The oligarchs there don't care that it's a shithole, because they get to pilfer most of what little wealth that shithole gets, so they are enormously wealthy and only ever answer to putin, who mostly lets them do whatever.

The same effect happens in little island nations with petty dictators or african warlords. People who pursue power aren't pursuing actual tangible things. They just want "power" for it's own sake. They get off on it.