@snacks @vriska @kaia True, that is a VERY rough estimate. I'm no longer in touch with people who do this, but I don't think the situation changed much. However there are dozens of popular games which can be categorised as e-sports, there are professional gamers who stream their online matches, they also have tournament prizes, some of them have advertisement contracts. Then there are people who stream the tournaments and provide insightful commentary — they also make some. Then there are popular entertainers who stream different games every time, who might also have ad contracts and make money on the side.
Overall they are not too few, but not many either. Even among the 10% the income varies strongly, some can consider that their primary source of income, some consider it a bonus — an opportunity to make extra to buy snacks and new games, but otherwise do it for fun.
But absolute most are either doing it for a few friends to spend some time together or are just wasting their time.
I believe it's more or less the same even in spaces like OnlyFans, this is essentially how this attention economy works: few success stories motivate a lot of people to do it, most of them end up doing it for free, and in case with OnlyFans destroy their mental health as a bonus. The latter isn't always the case — some manage to maintain healthy attitude towards it, others end up with it chipping off their integrity little-by-little, until they spin into a burnout and major depression, I've seen enough such cases.