Billionaires don't want basic income because billionaires no longer want there to be a capitalist economy with consumers.
In a capitalist economy and a consumer economy billionaires are completely dependent on those consumers for their wealth, power and prestige.
Think of it like this, let's say you lose your job and you can't find another but your extended family all chip in and keep giving you money that would bug you right?
You would want to be dependent on them. And let's say you didn't like your extended family. Let's say you had nothing but disdained for them. You would absolutely not want to be dependent on them and their Goodwill.
That's the position billionaires are in with consumers and employees. They are completely dependent on them. But bizarrely unlike you with your dependency on your relatives they have a shitload of money and power they can use to break that dependency.
So think of it like this, let's say you were a real asshole and you decide that you were going to rob all your relatives who have been helping you out blind so that you want dependent on them anymore because you had all their money. That's what billionaires are trying to do. Take everything for themselves and leave nothing. And then create a system where they never have to be dependent on anyone else again and everyone else has to bend over backwards worshiping them or else.