"somehow"... Twitch pays about $3.50 per 1,000 views to full-time streamers, starting somewhere around 500 regular viewers. Top end streamers make $5k/mo streaming 40 hrs a week. It's not SF senior dev money, but high-school me would think it's pretty cool to be making money "just" playing video games. (Instead I'm posting on HN for free.)

For many popular streamers it is indeed their job