If I'm driving and need to stop to use the bathroom, eat something, or so on I'm setting myself back time-wise. Plus I have to stay sitting down the whole time and have to stay focused on the road for hours.
If I take the train, I can get up, stretch my legs, grab some food, and I'll still get there at exactly the same time I would have otherwise. I can watch a movie on the way, or pull out my laptop to work on a side project if I want, or play some video games.
I'll take the train over driving any day.
But I usually want to have a car. So I'll be driving until it really doesn't make sense for me.
Most people I know spend crazy money for a car, if you compare to how little they could spend. Thus it seems many people are ok shelling out thousands of dollars a year for a cooler or more comfortable car. I have a feeling if high speed rail costs the same as taking their car, they are for sure going to take their car.
Even free can be more expensive than driving.