Rough riding through the Great Plains (CZ)

Having now made two Chicago–Denver round trips on the California Zephyr, I must say that the track through Nebraska and western Iowa is some of the roughest I've ever ridden over. Particularly disconcerting is the fact that this portion of the trip has occurred in the middle of the night on all four of my rides.

Has this always been the case? How exactly is BNSF beating their track up so badly?

At least twenty years.

Why should BNSF maintain the track for 79MPH? All they need is 60. Also, Nebraska has but 4 Congresscritters and vitamin (one a day) service. No political advantage to passenger grade maintenance.