Dirt Showdown was removed from digital sale on Steam a couple of years ago. As with most of these instances, you can still download the game if you own it, and it will continue to appear in your library. But since the library redesign, Dirt Showdown might look a lot less like it belongs among racing games, and a lot more like a way to hang out with some anime catgirls.
The new Steam library includes a big background image at the top of each individual game page. For some as-yet-unexplained reason, Dirt Showdown’s header is an image from the 2015 visual novel Nekopara Vol. 0. Players on the Dirt subreddit discovered this a day ago, and since then, people have been noting plenty more oddities.
In my own Steam library, Metro 2033 is headlined by an image of Max from Life is Strange. The PlanetSide 2 test server features an anime girl I’m not familiar with getting very intimate with someone’s ear.
That test server doesn’t seem to be in regular use at this point, and Metro 2033 has been replaced by its more recent Redux, so it looks like disused listings are subject to this glitch.
For now, just enjoy your time with the catgirls.