In the majority of US cities, bus networks are optimized for coverage instead of frequency. A bus route might only run a few times a day at commute times - but

In the majority of US cities, bus networks are optimized for coverage instead of frequency. A bus route might only run a few times a day at commute times - but city planners can check the public transportation box for all the neighborhoods along the route. With that methodology, it becomes impossible to reach a destination that requires a transfer or get to a job at an off time. Therefore anyone with the means to avoid the bus will. Of course some cities have BRT routes, dedicated lanes, and high service frequency. If you have access to a bus network like that, indeed it can operate as well or better than a rail system (and often at a lower cost). But that is the exception in the US, not the norm. Whereas most commuter and urban rail in the US operates with high frequency and dedicated right-of-way. Hence the presumption that buses "don't count".