Ah, you must live in one of those... whaddyacallem... cities.~

Roadkill is very often eaten by something, though if a human wants to do it, they have to pick it up before the county gets to it. After that, it's literally off the table. The exact method of disposal depends on jurisdiction, but some places have a sanctuary or research facility for carnivorous species nearby.

A random dead deer in NW Indiana, for instance, might get picked up by Wolf Park research facility, stored in their freezer, and fed to the main pack (still frozen).

Dead horses were picked up by knackers and turned into dodgy sausages all the time. This was just one of the unsafe food practices that led to the establishment of the FDA and public health inspectors.