What on earth are you talking about? This is like the opposite situation. On PC of course mouse and keyboard has excellent support, it's usually the controller support that is lacking and why Steam has to have labels for "Partial Controller Support" and "Full Controller Support" because it is not a given that it will be there right out of the box. Hopefully this data will be used to convince devs to integrate better controller support as they learn that not everyone wants to play everything with a m/kb and that a ton of people still prefer a controller.
I'm talking about the massive amounts of posts here everytime this topic comes up acting like m/kb is some outdated archaic scheme that only a crazy minority uses when these stats show us that even for third person action games more people still use m/kb. Look at the posts in this thread alone with everyone rushing in to say how they only use a gamepad and would never play with m/kb, it's a bubble and that's what these stats are showing. Which is why they might be surprising for some people who never get out of that bubble.