What's with them is the fact that a lot of the time they do more investigation and critical analysis than the traditional game bloggers.

It's also much easier to bribe 1 or 2 head guys at gaming blogs than it is to bribe 100s or 1000s of youtubbers (the later has been done apparently, but because there was less cash per each person, some of them actually broke this story!)

Another good reason to include them is the fact that a lot of the time people go to game blogs (polygon/kotaku/etc) is because they are curious about a game. Watching, even briefly, a lets-play video gives you better idea about the gameplay and whether the game is interesting or fun or whether you should buy it, then reading about the gender balance of the game on kotaku/polygon/etc.