Many countries have Jitney buses. Tiny micro-buses that can do more local bus routes and run more frequently.
Of course, there are several things that make them difficult in the USA including population density, wealth (people like cars), and cost of wages.
Good for small towns with limited destinations, but they could likely work with dropping people off at express bus routes in larger cities.
Nonetheless, I'd rather see a 15 passenger van stuffed full than a 40 passenger bus cruising around with a single passenger.
At a minimum, the after midnight routes could shrink their buses, and thus have safer and more fuel efficient vehicles.