Demand fluctuates relative to amenities, jobs, goods, services available on either end of a thoroughfare. If people like the offerings in one metro area vs another, or in a suburb vs a larger city, more people travel to and from that place. If they have things they want to do in their own backyard, they do not do that. The distribution of all of those things changes over time because of course it does.

Thus the law of conservation of traffic flux is violated and none of your conclusions are sound.

Sure sounds like public transit design is a red herring, no? :o)