Thread: Closing the gate ahead of scheduled departure time

I missed an important flight recently, even though I had arriaved at the airport 1.5 hours ahead of the departure time. Things beyond my control happened after arriving at the airport, and I got to the gate exactly 8 minutes before the scheduled departure time.

Not sure if the airplane was still attached to the jetway, but the gate was closed. The agents said that I was supposed to be at the gate 10 minutes before departure time, and no dispute there. But, trying to understand why they would close the gate when they knew that some of us (my guess is that we were all nonrevs) were somewhere between the self checkin kiosk and the gate. The agents seemed nice enough people. This was the only flight all day that had empty seats.

Of couse, we don't want to inconvenience the paying customers. So, made no fuss, just returned home. But, I now have to wait months to reschedule my medical appointments again. For future purposes, I'd like to know the proper protocal in this type of situation. I am also curious if there is some sort of policy to close the gate as soon as all paying customers are on board. Thank you in advance.