As a gate agent, I can tell you there is an immense pressure to get a flight out on time. To wait for a late nonrev who may not show up is absolutely not a reason to keep things open and risk a delay. We don't know your reason for taking the flight, and frankly don't really care. I'm not sure what your airline background is, but if you haven't worked that side before I assure you that for everything you see happening, there's at least just as much happening that you don't see. Flight attendant paperwork to deliver, cargo information to give to the pilot, last bags to put on... adding another person would likely mean having to restart the process, and what is usually perfectly timed to get done in 10 minutes is a lot harder to do in 6-7 minutes (there's a good chance the flight is also closed out, so boarding wouldn't be an instantaneous process anyway).