They are not blocked by cars most places they should go. suburbs with no traffic are dense enough to support bus transport with reasonable frequencies, but they don’t get it.

There are a few roads where buses are blocked by traffic. However those roads have (or would if the buses would actually go anyplace other than those roads) enough demand that they should have a fully grade separated train on those routes (or often just off those routes and no service at all on the road itself - get the transit closer to where people want to be)