There's barely any games.
Yeah, there's "some" games. There's maybe 5 games that are actually worth looking at that aren't crappy "so retro" pixel platformers.
Doesn't help that Ubuntu still doesn't have Steam in its software repository even though Valve changed the license to allow it to be bundled in repositories.
They have a repository with Skype, what the hell.
It would be useful if Valve split "Other" into 3 different entries: "Other Windows", "Other Mac" and "Other Linux". It would clear up a lot of ambiguity.
As to Steam in the repos, you may have to get it from the Ubuntu Software Center, as it is a 3rd-party application much like most of the games for sale. I don't think stuff like that shows up for apt/Synaptic, so you have to use USC to get it.
I wouldn't be surprised if (at least some of) the decline is due to many people getting excited to try it out, and now that they've tried it, went back to using Windows.
indeed ! personally, i don't keep Steam running while not playing and don't play much these days. and with it not minimizing into DE's tray, i won't be surprised if lots of other people did the same, which would decrease the statistic.
and i'm also using wine+windows's Steam & occasional reboot to windows to play non-native games.
Just to clear things up a little, this is a survey, there's nothing automatic about it; they literally ask a small group of Steam users each month to submit to the survey.
Unfortunately we're in the dark about the exact methodology being used, depending on how users are selected for the survey the results may be skewed in either direction, and there's also a question about how they round the results.
Just think: if the survey was given to 1% of the world during one hour once every month, depending on what hour they pick they may end up with very different results as different countries would be asleep and some countries use Linux more than other countries.
I'm not saying that this has happened, but that it would be very hard to write a manual survey that avoids these biases. If the survey was automatic and real time, I'm sure everyone would be up in arms about their privacy being violated.