It's extra work to get the timer working, and without an autosplitter you're manually timing it which is gonna have its own inaccuracy anyway. Mods/verifiers are gonna time it independently which makes the timer in the video less useful.

The only justification I can think of is to make sure the submission video is not sped up using LiveSplit or such, but if I wanted to cheat like that I would just add a different timer in post-production.

Am I missing something here?

Not sure if I'm missing something in the rules, so asking here.

For example, playing Outbreak using Reapers makes for a decent strat. But you get Reapers from the Tosh missions.