My first guess would be a combination of insufficient demand for faster playback than that coupled with UI concerns (limited set of options provides more ways to display them) and perhaps processing concerns. (however probably not the last one)

why watch faster?

Median fast speed that human mind can comprehend 🐶🐾🫡

web-video constant probably

Bc there is only so much coke a person can do before they od...

They should at least match Spotify at 3.5x

Consumption rate is capped~ otherwise web2 cdns would burn up.

When do you need anything over 2x speedup?

Newpipe used to allow 3x