So why does it bother you?
If it doesn't harm you in any way, what do you gain by adding a clause ?
There are people who buy without reading anything, but you have a group that won't buy if there are DRM or abusive clauses, and a clause that prohibits uploading gameplay videos will be perceived as abusive.
I don't see it that way at all. If it only shows a few seconds of your gameplay, then anyone who's interested knows they should go find information about it, because that video doesn't go into depth. Ultimately, it's just a showcase, not an analysis or review of your game.
You can't expect all content created about your products to be good/high-quality; that's the problem with social media.
The problem with putting a clause that prevents anyone from uploading gameplay of your game is that you're not only preventing people from creating bad content, you're also preventing people from creating good content, and in a super-saturated market, it's like shooting yourself in the foot.
