While there are federal repeaters out there across the US. Most fed frequencies are simplex radio to radio. So that would explain why you can only hear them at or by the bus station. I believe they also use Mobile Repeaters onsite of locations they are at too.
That might be true for agencies that don't have much of a wide field presence because they are primarily administrative. For agencies that have work to be done in the field and are quite some distance from their offices they don't use simplex often, except when field units are close to each other. Land management agencies and military bases have a lot of repeaters in their systems. Customs and Border Patrol (CBP) has an extensive system of repeaters over a large area. The Army Corps of Engineers have many repeaters to operate dams, locks and reservoirs. The latter having significant recreation use requiring park rangers in the field. They manage a significant amount of lands around their projects. The Coast Guard has quite a bit of radio traffic, most of it simplex, primarily along ocean shores.
I've lived in rural areas for the entire time programmable scanners have been available. I don't have much experience listening to federal agencies in a city. When I'm in one, with most of that in western cities, I listen to the federal land management agencies. All of the major cities in the west are in listening distance to such agencies.
Depending on your listening preferences and location there can be a fair amount of federal agency traffic.