>>102119619Great art style that makes it easier to stretch and distort characters without it looking really forced, but it's not cartoony to the point the characters are featureless or you can't do something more serious with it.
The characters all have really unique, distinguishable and easily identifiable designs and personalities, and you can either use the existing characters and exaggerate their personalities, or make up new ones using the game's assets.
Lots of opportunities for sentence mixing.
Hundreds of costumes, maps, sound effects, and other tools the game just gives you.
The different styles and approaches to the source material that individual creators have that lends the videos a more unique personality.
In general, the game is really funny and well-designed so it gives you a lot of creative freedom with it that you just don't get with other properties that take themselves more seriously.
And above all, memes.
Garry's Mod came out just before YouTube as a platform was created, and so the TF2 videos have always walked hand in hand with the site's culture and, by extension, it's memes. The game is full of memes that themselves can lead to other memes, either forced or organic. It's a self-sustaining meme cycle.
It really doesn't matter what state the game is in now or whether or not people left it for trendier, newer games, people are still going to be making TF2 videos years from now because it's a part of Internet history that can never be taken away. It's transcended the game and attached itself to the lifeblood of meme culture.
Creators may come and go, the popularity of these videos may have it's peaks or lows (right now we are actually seeing more of these videos than we were a few years ago because of newer creators and newer memes for them to lampoon), but they are not going away for a long time.