They've been developing their marketing strategy for years, beginning with their signature campaign, promo codes on Twitter, social media giveaways, and monthly (?) art contests. Roobet also organizes games for the bitcointalk community, which can be found in the Games and Round section. And, as far as I know, they've gained traction from Twitch Streamers.

It's also not surprising that so many people are drawn to play alongside Roobet. I've also not encountered any issues on their end in terms of receiving their art contest rewards.