> Seems like the far more plausible reason is that drivers don't want to be held up by a cyclist traveling at 10mph in front of them?

You sound like one of thos drivers who believe it's OK to put other people at risk to save themselves a couple of seconds.

I see this all the time in my large truck that I'm very good at coasting into red lights. Even when there are already vehicles stopped at the light, people will not only stay on the gas way later than necessary and then brake unnecessarily hard but will also pass me to be sitting one car length further ahead at that light. Often it is done dangerously, without turn signals or proper blind spot checks. I know this because I've also almost been hit repeatedly on my motorcycle by cars doing this.