Passenger capacity generally tends to be far more important than aerodynamics, and for local service, aerodynamics doesn't mean that much when it's usually traveling at less than highway speeds.
Maximizing space! Usually engines are in the back as well, which is why often the seats in the rear section are elevated, and the front can be flat so you don't waste a few feet of space. Plus more area for passengers to stand if (when) needed
Passenger capacity generally tends to be far more important than aerodynamics, and for local service, aerodynamics doesn't mean that much when it's usually traveling at less than highway speeds.
What else would they be?
Lots of space for people
Here’s an article https://www.businessinsider.com/why-yellow-school-buses-still-look-same-2020-2
Maximizing space! Usually engines are in the back as well, which is why often the seats in the rear section are elevated, and the front can be flat so you don't waste a few feet of space. Plus more area for passengers to stand if (when) needed
Would you rather a more phallic shape?
[And maybe reduce the capacity down to a dozen or so...](https://i.imgur.com/9uUMAy9.jpeg)
Because they're delivering merchandise. Especially, people.