It wasn't too long ago that I'd posted about how Ubuntu seemed well on its way to becoming the top choice distro for basically everything, including gaming. That was before Canonical shat their own bed, though, announcing that they were dropping support for the 32-bit libraries that PC gaming generally, and Steam particularly, depended on. Valve, which had been recommending Ubuntu as the preferred distro for Steam, withdrew that recommendation; and while Canonical apparently walked back their decision on those 32-bit libraries, Valve's recommendation was not restored.
And now, just a few months later, we're starting to get a good look at exactly how much damage Canonical/Ubuntu did to their own cause with PC gamers, thanks to a great post at Boiling Steam, which sums up the trend with this chart: