I'm starting to think that most journos don't think the average gamer wants to read about the PC, no matter how many PC gamers there are. There's just this hobbyist-machine image problem the PC has. The public is scared of doing anything with its PCs. My dad, who actually kind of likes games, will sooner play a game on his Android phone than play a game on the hand-me-down gaming rig I gave him with Steam set up. And there was that one article a while back about why barely any PC gamers are in Japan where a guy basically said he doesn't play games on his computer because he didn't want to burden it with "unnecessary stress." And then there's the general (correct) view that console gaming is more accessible than PC gaming. Put all that together, and it's easy to get stuck in the "this is niche, so it's bottom priority/a specialist will cover it" mindset if you're stuck in the idea that a normal gamer = a normal person who happens to play games on console.
Some people have suggested conspiracy, but simple biases are a simpler explanation. Sure, a journo might say "oh, I should cover PC games more" if they did an analysis of the market and what they wrote, but who does that when you can lean on your gut?