I've found with the food stalls that they only perform well, when they are placed outdoors. I thought maybe it was location at first, but I did a couple of experiments. I placed food stalls really far from campus outside, and stalls indoors, close to facilities and the assistants preferred to tend the ones really far away outdoors and the students would follow. My second experiment is having the same stall one indoors, one outdoors, virtually next to each other, and assistants would seldom stay at the stall that was indoors, where the one outdoors would have a queue of 30. Doesn't matter how many assistants I have, or if I assign them to only sell food and drink, they wont tend to the food stalls for very long when indoors, even if I place them in them myself. 

Hey Natini!

Thank you for providing this information, I shall pass this along to the dev team for further investigation, it does seem a little odd!

Thank you for your patience!
Jax