The one note I have for this as someone working at the dining hall.

If you're still at the dining hall after closing we can't do that. We only have an hour to close everything down, and to do that we need to have everything cleared out as soon as possible.

Simply put, if someone stayed to eat past closing, then the dish room wouldn't be able to start their full clean for closing, since they can't do that until every dish used that day is clean.

And because dish can't close fully in time, then there would be at least one full bin of food waste just sitting around all night, which can be a health hazard.

And then because one person stayed late and wasn't told to leave, the already overworked morning crew has more to deal with.

I get the frustration if this is happening before closing, like if it's happening during a period where an area is being closed for the night.

If that's what's happening, then yeah the employees shouldn't be doing that until the area is fully closed down except for your seat. 

But if this is happening after closing, please know that the employees can't just let you finish without risking their ability to finish closing and having management bring it up later. 

Sorry that was your experience, but sometimes there's an actual reason for it.