There’s a lot of reasons most likely, though, it’s just that the bus you caught is one of the shortened routes. They’ll have buses/trains do half the route and turn around to increase frequency of that route. Usually doing the full route around times when more people are going all the way. Sometimes if you check google maps it’ll tell you to catch a bus that comes 5-15 minutes later than the one on the septa app that says it’s coming next based on your destination. Not all busses are like this but for routes where not a lot of people are usually riding it’s better for them to just drop everyone off and turn around to be ready for the long trip.