What's the reason that sim racer's arent selling as previously? I'm generally curious? Same ole, same ole?
More competition from other racing games on the PC especially geared towards hardcore sim games, the release of games with modes and systems designed to keep you playing for years (Destiny, Overwatch, Rainbow 6 Siege, Call of Duty, FIFA, NBA 2K, etc.) and also people getting fatigued by the same IPs being released time and time again. Even Activision stopped numbering Call of Duty titles and are now numbering subtitles, because they know even the name followed by higher number can get people fatigued just because of the meaningless number.
There gets to a point where people start to wonder why they are playing the Fiat 500 Abarth 3 lap race around Barcelona for the 10th different time against AI just so they get credits to unlock the same car they unlocked in previous games. Of course new features get introduced in new games like rain, dynamic weather, day and night cycle, but it gets to a point where the core experience is so similar, that you start to question yourself, "Why I'm getting a new iteration of the same racing game IP while you could be playing the game I already play and own aka Destiny/Overwatch/PUBG instead?".
In the "old" days, racing games were the games people got to get them replay value, because multiplayer wasn't a popular thing outside of PC and most games were single player campaigns without any meaningful replay value. Now almost every game is built to give you that replay value and keep you logging in every day. Racing games can still be a factor and have a big userbase, but they need to adapt to the new reality imho. Arcade racers like Forza Horizon, Driveclub, Need for Speed, The Crew are the only ones that should have more than 1 release in a single generation from now on.