I noticed this as well. My guess is that most people who are streamers or who make gaming related content already have revenue from ads and subscribers and whatnot on other sites. There probably isn't as much incentive for them to begin using a new platform.

That, and, like you said, Steemit attracts people who are interested in crypto first and foremost. I'm sure as the userbase grows, so will the number of people interested in a wide variety of things, gaming included.