Newton's 3rd law: every action has an equal and opposite reaction. Literally everything moves when a load is applied to it, including roller coasters. Certain rides tend to flex more than others for various reasons, but let's remember that these engineers are good at what they do. They've analyzed every inch of track, accounting for load input, fatigue considerations, and factor of safety, and determined that the train load will not yield the track at all.
The good thing about using steel as a building material is that it exhibits what's known as a fatigue limit, which really isn't what it sounds like. Essentially, steel weakens as it's cyclically loaded based on a number of different factors until it reaches a certain point where it just doesn't get any weaker. At this point, the object can theoretically last forever but external factors, like rain and corrosion, tend to force situations like we saw with The Incredible Hulk.