I've seen that trend too, especially when I go to the gaming section of YouTube. I think it's because that GMOD and these other titles are popular at the moment and people want to join in on the fun. Not to mention that a lot of big YouTubers like to play some of these games as well, making them even more interesting to play. As for me, I would never record a gameplay just because it's popular. I'd have to actually like the game to record, that's why a few of my first gaming videos on my channel were games that I recorded from the PS2.