My guess is because it doesn’t have a direct line to the destination, so you need to go all the way down to a station and make a bus swap to come back.

Like imagine you need to go two blocks south, from First Street to Third Street. But there’s no bus that goes north/south. So you go fifteen blocks east on First Street to the station, wait for your next bus, then come back another fifteen blocks west on Third Street in a new bus. Or you could just walk the two blocks south.