Most North American road infrastructure has been rebuilt over the last century to be automobile-centric. "We" deem that conflict to be acceptable because the alternative is more complicated phasing - most of which results in delays to car traffic (and pedestrians!), and so most places won't accept it. For details, here's [1] a document that outlines the tradeoffs in various different signal phasing designs.

TL;DR is that "we" won't prioritize any road user except the automobile.

[1] https://ops.fhwa.dot.gov/publications/fhwahop08024/chapter4....