I fly because it's fast, not because I like airplanes. Even the fastest train is way too slow to replace a plane for a long-distance trip. Then for shorter distances cars win out because of how convenient they are. There's no niche for passenger trains except for commuting into urban areas with no parking.
It doesn't help that in the USA train tickets seem to cost more than plane tickets. I think I'd still usually fly even if the train was free, so I'm certainly not going to pay extra for a slower method of transportation even if it is a little more comfortable.