Unironically, it wasn't because he fucked up the machines. It wasn't because he got too greedy. It wasn't even solely because he set two of those casinos against each other.
It was his fucking ego that did it.
He had them spend absolute shit tons on big shows, flashy displays, all that shit. So much that even a casino couldn't keep it up and went into debt doing all the events he kept forcing on them to show off how cool and wealthy he was. So they had to keep borrowing money to afford them, which meant they kept sinking deeper and deeper into debt until they went bankrupt. It didn't help that some of his main casino execs, who would've probably told him to knock off all the glitz and glamor so they could break even for once, literally died in a helicopter crash in the 90s and were never replaced. Plus he kept fucking with gaming officials to try and get deals, which of course they weren't amused by, leading to him getting even more screwed. But if it was primarily his fucking obsession with big events the casinos couldn't actually afford that eventually sunk him.