I suggest that there should be a subsection of survival runs split between co-op and solo where you speedrun a certain wave, an example would be the timer starting when you are able to move and the timer ending when the wave hits the number, like 15, 30, 50, 75, and beyond. I'm on vacation so i can't record an example, but if you want I can record one when i get back.

Why was this never added?

Answered my own question: https://zombiesworldrecords.com/leaderboards/mw3/high-round-survival

Because this was 6 years ago and we only added survival last year.