The issue is that becoming a billionaire has more to do with being lucky than it does with direct exploitation.
If everyone in the US chipped 5 dollars into a pool, and it was randomly given to one person, that person would be a billionaire.
And yes, they have a huge concentration of other people's labor represented in that cash. But the person who won the pool isn't a bad person because of that. They didn't exploit anyone themselves. Just because someone somewhere at some point under capitalism was exploited, that doesn't lay the moral condemnation at the feet of the lottery winner.