PC is a little more complicated than X killed it.
The performance issues are a HUGE one.
Lack of competitive matchmaking is another big issue. Competitive playerbases are massive on PC, Twitch loves PC players, and people expected either ranked out of the gate or in the near future at launch.
Lack of proper matchmaking in general was another turn off, though that is not a PC specific issue.
Steam’s sales are also another factor. Steam hosts sales many times a year, not even considering other outlets like Humble Bundle or their smaller deals, so many PC players will hold out for more expensive titles. This means the initial reviews and the subsequent releases that followed BB had more time to sink in, and they did their toll.
I guess a lot of it has to do with PC players expecting more in general. Not to say console players have low standards, but dedicated PC players tend to be a very high standard group by comparison. It’s like my professor told me, PC gamers are the ones who want the very best, who don’t settle and willingly spend the money to get that. The same can be applied to our standards for games.