Bus no. 31

I seem to be spending a lot of time on this Jekyll and Hyde bus line. So much so that I might get a permanent seat/​sleeping bag on it.
It’s not a bad and the bus are usually quite clean. The only thing I don’t understand is that there is never a happy medium on this line. Either they come super often and empty (usually off peak, 10−4ish), or you have to wait day and night for a crammed one (before work and after work). Also, the bus drivers are either super friendly and happy, or mardy as heck.
?!? Is there rhyme or reason to this behaviour? Oh well, at least it hasn’t dropped me off somewhere I didn’t want to be yet.