There's actually a lot of folks who stream themselves gaming, a good number who do it full time, and a lot more who do it part time for extra cash. Lots and lots who do it for free or tips.
On twitch you share the sub fee, so you get 2.50 per sub and twitch gets 2.50. Get yourself a few hundred subs and it's not a bad gig. And that not even counting donations/tips. The better guys with 2+ k subs aren't making horroble money.