From Softpedia:
The free Windows 10 upgrade promo that Microsoft offered in the first 12 months after the launch of the operating system had a massive contribution to its growth, especially in the gaming industry where the majority of users upgraded their computers.
On Valve’s Steam, for example, Windows 10 improved at a really fast pace, overtaking Windows 7 as the number one operating system for PC gaming.
But figures provided by the company for the month of January 2017 reveal something that almost nobody could see coming: Windows 10 has started declining just when it was so close to reaching 50 percent share.
Specifically, Windows 10 dropped 0.48 percent last month to 48.49 percent, but it continues to remain the preferred desktop operating system right now on the gaming platform. Windows 7 64-bit is the runner-up with 29.74 percent, up 0.72 percent over the previous month, while Windows 8.1 64-bit is far behind with 8.14 percent, down 0.31 percent.
The 32-bit version of Windows 10 lost market share as well and is currently at 1.18 percent, down 0.04 percent from December 2016.
For whatever reason, Steam was the one market where Windows 10 really had managed to overtake Windows 7 as the top choice of PC users, and this month's change is small enough (<0.5%) that it could just be a transient blip. But even if this isn't the start of some kind of trend, it does send a clear signal that the easy Windows 10 converts among PC gamers have all been converted; from here, it gets only harder for Microsoft to win new converts.
It's also noteworthy because this is, once again, the opposite of what the overall OS market is doing. Just as Steam bucked the trend for Windows 10 adoption until now, with gamers switching to the new OS faster than PC users at large, Steam is now bucking the trend again, retreating from Windows 10 just as the new OS finally starts to make gains in the OS market overall.
This may be why Game Mode was rolled out so early: i.e. before it's actually working, or at least before it's working well enough to actually produce performance gains for non-UWP games. Microsoft seemed to be concerned about Windows 10 adoption stalling out among users who had been the first to embrace the product, a concern which now looks like it might be justified. It's unlikely that Windows 7 will regain enough market share among gamers to regain the top spot, especially now that it's not available for sale anymore, but if Microsoft are serious about reaching out to Steam gamers and keeping them on Windows 10, they're apparently going to need to do better than "GFWL2."