I don't know all of the underlying issues but I would imagine having initial access to money to buy top-flight PC equipment and also the types of games that people play. I'll address both.
I'm the only black person that I know personally that has dropped more than $1000 on anything gaming related in their life at one time. My current PC, built in 2012 is a low tier PC now and I spent over $3000 on it, not to mention the additional stuff that I have hooked up to it. That's a lot of bread for someone to come off of to play most games that a $400 console can play too.
Next would be the types of games being played. I look at my gaming collection now and it is far more diverse than it used to be. I used to get sports games, action/adventure games, platformers... Basically, what was popular on console. I didn't really get into Civilization until V. I've always played Sim City but I was just largely trying to play console games with better graphics on PC for the longest of times. Tried to get on the Counter-Strike wave, didn't particularly care for it. My teenage self wouldn't have purchased a Starcraft, Diablo or XCom. I have them now. I got on the FPS wave with Goldeneye on the N64. It wasn't until later where I doubled back into Quake, Doom, Wolfenstein, Unreal, etc... My first FPS on PC ever played was Wolfenstein because my uncle had a shareware copy but the first one I bought was the first Thief. Think about when we would be in school, EGM, Gamefan, Next Generation mags would mostly feature console games, that's what we were primarliy exposed to. It wasn't until I got older to where I started to look into PC Gamer mags and learn some shyt myself. Less hand holding in the PC world. What brought me back to Steam was TrackMania United, at the time, a racing game exclusive to PCs. Lack of info, knowledge and money I'm sure contribute.