It's a chicken and egg problem. The way to make buses competitive is to build bus only lanes. But to do that you end up removing a lane for drivers and dedicating enforcement resources to keeping bus lanes free of private vehicle traffic.

The usual pattern is when a bus only lane is proposed, drivers complain because they view the bus as a social program. Local legislators often take the drivers' side because they also view the bus as a social program. Even if you get the political capital to push a bus only lane, traffic enforcement will routinely ignore bus lane violations. LA is making waves on the latter problem by attaching cameras to buses which automatically write tickets for cars blocking the bus lane.

Ultimately it's a politics problem. If nobody wants to spend political capital on running a bus system as a transport program, it ends up as a social program.