How many users of those games are actually playing on Linux? Genuinely curious because I doubt it's more than 10%.

There aren't many stats on actual Linux usage for cross platform games. The only public data is from Humble Bundles, and it was for indicated usage (i.e. you could select what platform you intend to use the game on while buying).

Even if it's 10% - it's a lot of users.

There was some article, that availability grows gradually. I.e. if too many games will come out for Linux at once, the market will be too flooded with them, which will in turn hurt both developers, and users.

Probably 1% or less (based on the steam hwsurvey).

Considering the share that Linux has on the desktop, this is hardly a surprise.

Steam survey doesn't show percentage of usage per OS for cross platform games. At least I've never seen such data published. It's tossed around often, but it's not useful really.

That's true. However, I'd wager that the data would still correlate with the hwsurvey results. Would be interesting to see the actual numbers, especially for CS:GO and Dota 2.

I don't think it would. I saw some reports from actual developers, that differ quite a lot from that survey. So, I wouldn't use it as any sort of definitive metric.