Exhibitions haven't taken off because there isn't actually that much potential for them. The people who think it would open up a whole new world of possibilities are just imagining things.
Most possibilities of entertainment have been covered by the actual speedruns, and those that haven't aren't really enough to justify a
whole new movie. Sure, you will find a game
here and there that is an exception, and when you do, go ahead and make a playaround and post it! The problem is that there
just aren't that many games where this is worth doing where it would feel like you're not just treading old ground, but slower. Movie clip compilations on YouTube are a lot more appropriate instead, rather than having the buffer of playing the rest of the game in between the interesting parts, and expecting it to get published on a site where everyone's base attitude mismatches with yours.
If you disagree with this statement, then it is simply a case of your base attitude not matching with mine. In that case, make some exhibition runs and prove me wrong, maybe they'll get published like the above movies I linked to. But I'm willing to bet that, if you actually get down and honestly try to do this, simply finding a
game to provide an example is harder than it sounds.