Yes some is luck, attractiveness, etc. But that's true in all careers.
Just because they're playing games doesn't mean they aren't working. Athletes get insane amounts of money to play games. They exert themselves more physically, but I expect being a top steamer day in and out isn't a cake walk either.
Unless you're an absolute god at whatever game you're playing, nobody wants to simply watch you play a game. People come for the live commentary and audience interaction.
Being a successful stream takes charisma and cleverness, and being clever and charismatic for 3+ hours straight to entertain your audience can be exhausting.
Wealth is not linear, it's not promised as the result of "hard work". Hard work helps, but it isn't the determining factor of whether or not you'll get a payout.
You must work hard in a domain that has public visibility and actually produces something of value to people. And yes, Basketball (and watching it) is extremely valuable to a lot of people.
Nevertheless, anyone that manage to have 5+ millions USD in property and savings before they are 30 got to a level of wealth in 10 years that 90% of people will not achieve in a lifetime.
I am not saying at all it is not deserved. I am quite ok with them earning millions. But it does make a lot of us pull this comparison, both in achievements for humanity and in effort spent in their endeavors.
I personally never played or wish to play the fame lottery, I prefer the hard work path.