The experience I shared was on a city bus.

My point is that you're totally disregarding everything a bus does to stop apart from waiting for passengers to board and de-board. At the very least it has to slow down, then accelerate. Half the time it has to swing the ramp out, which takes forever. Maybe someone has to load or unload a bike. Then it has to re-merge with traffic, and maybe every 10th car will let it in, so that can take a long time too. I don't even know if waiting for passengers is _half_ the time spent, let alone all of it.