Why?

Relative inactivity

The original intent of city segments was for them to emulate shorter portions of Any%, but due to constant changes in the route it was impossible to keep the segments accurate. An example was using trucking in Badlands to save time in San Fierro, the Badlands WR was impossible to achieve if you were doing the new route.

This and the fact that almost all of the top runners didn't really care for them made it an easy decision to remove them.