At insane income rates money is a means. For most people it's as an end, how they survive, but past a certain point it the ends are nicely wrapped up and become afterthoughts. There's a lot you can buy with ever-increasing money supply, but at some point you can also afford or already own most of these things. Thereafter, the point of money is the pursuit of that which cannot be directly purchased. For many this takes a philanthropic route, donating unneeded portions of their wealth or income to their charities or goals of choice. For some--and, I think the majority in future filled with AI workers but no universal income--it's about control.
There are many ways to control people directly with money, by paying them to fulfill various desires. It's surprising what some will do for money, particularly if they are in desperate need. But a single person could reign heavily over a thousand people by being a CEO of some busybody company. Control their schedules, who they meet with (and when and where and for how long), what they spend the majority of their day doing, and you don't even have to pay them that much. The rich will control the government, of course, and so worker protections go out the window and now all employees are considered always on the job (and thus under that much more control.) This is a more direct control than simply paying them to do whatever (it's surprising what people will endure to stay employed, things beyond what most people would be willing to do if told directly, at least at a moderate income level.)
I think this outcome is far preferred by the lawful-evil rich, as opposed to maintaining small personal armies to stave off riots and raids (an army that could turn on them), or being forced to share the money they "earn" with the government (who then redistributes it to the people.)
(If you think that sounds soul-sucking, an alternative but not-completely-exclusive outcome is that common people are used as lab rats in medical trials for drugs and procedures that keep the rich fit, healthy, and grant longevity.)