They aren't paid to be good at games, they're paid to tell us about them, so it ultimately means nothing. Getting more into the science of it though, I don't know how I'd feel at a big event with constant noise, people right next to me -- some of them possibly dressed up as Sonic the fucking Hedgehog -- whilst playing a game, whilst thinking about what to say about the game as I'm playing it, whilst standing up (that's our Kryptonite, man). My guess is I might not be quite as good. It's not always like that, of course, but they're usually not in their ideal gaming environments.
Outside of the performance anxiety that can occur playing games publicly, some people just aren't very good at them. That's why there are difficulty options and such. The controllers we use become third arms once the right amount of time has been sunk into games, but if that learning quota isn't met, you're fucked. It's time, always time. I think I read that it takes a minimum of 10,000 hours to become fully proficient in any craft.
A lot of people in the industry plain love games and just want to talk/write about them. I would hate it if one of the criteria for becoming a games journalist or whatever was, "Must be good at games." On the other hand, I have had the same reaction: seeing someone play a game so amazingly badly that you have the urge to switch the machine off. In my head that makes the same sound as a heart monitor when the cable is disconnected.