It's not that the train isn't pushing down on the track, it's that the force created by the unsprung mass is several orders of magnitude higher than the static

It's not that the train isn't pushing down on the track, it's that the force created by the unsprung mass is several orders of magnitude higher than the static force. The wheelset force is higher than the static force because the primary and secondary suspensions allow the wheels to move independently of the vehicle body. Imagine you have a 2x4 wood beam suspended across two blocks, with a 200-lb man standing in the middle of the beam - the beam will clearly sag in the middle. But if you place a 50 lb girl jumping up and down on the beam next to the man, the beam will sag significantly more. If you are looking at the effects of forces on that beam so see how it bends or breaks, it's the dynamic forces from the jumping girl that will control things, not from the heavier guy. At this point I don't know how to explain things without jumping into two degree-of-freedom mechanical models.