Because you can't get that much without exploitation and refusing to share.

There's no moral reason to have that much money. If you earned $2500 a day (about a million dollars a year) it would take you just under 1200 years to earn a billion dollars. I personally believe you should earn more if you work harder than others but there's simply no way anyone could work hard enough to deserve more than anyone should make in 15 lifetimes. If you are lucky enough to get that amount of money there's no moral reason to keep it all.

Now think about how Bezos is worth 192.4 billion dollars. Hopefully that helps folks understand the problem. And by problem, I mean the largest threat we are facing to human existence. Every other issue we're having stems from the fact that billionaires exist.

Say you work on a team with, say 50 people. Everyone works hard to generate money, but you're the star of the show, so naturally you get to keep a little more of that money than everyone else. The question is, how much? Is it morally questionable to make double what everyone else does? What about 10x? What if you keep half for yourself, meaning those 49 other people combined make the same as you? Not enough? What about 100x as much as everyone else? 1000x?

Taylor Swift's salary is about 1,700x the average in the music industry. People on her team are likely struggling to make ends meet or pay for hospital bills or support a family. Meanwhile, Taylor Swift is hoarding money like a fucking dragon.

A good person would never make it to a net worth of a billion dollars though. A good person would give away 999,999,000 to charity, for example.