Well, I've never seen one reopen the door, and any that do are breaking their company policy. When was the last time you saw a gate agent reopen the door? Has it been a number of years?
In my experience, the time that you have to be there before the gate closes is printed on your ticket.
Airlines need to do their best to keep to schedules. They might keep the gate open a couple minutes later if they know a passenger is on the way, but it is completely reasonable for them to set a time and stick by it.
Reopening the gate takes time for the flight crew that are supposed to be readying the plane for take-off.
If they hold up a flight, it has ripple effects later in the day.
I can understand and relate to it being frustrating to miss a flight, though in most cases the person I had the most reason to be frustrated with was myself.
If you don't want to have to worry about missing connecting flights, pay for a direct flight if one is available.
If you want the airplane to be flexible to your schedule, charter a flight.
If you can't afford those options, learn to deal with the reality that the airline can't hold up a plane full of passengers just because it is inconvenient for you.
“When was the last time you saw a gate agent reopen the door?”
How about last week for me? I got to the gate 15 seconds after the door closed (I saw it closing) and they reopened it. It was the last flight out for the night and they would have had to give me a hotel voucher since it was there fault for delaying the inbound flight. I’ve also seen them reopen the doors a number of times on international flights. I’ve never seen them open a door though once the aircraft door was closed, except once on an international flight.
“In my experience, the time that you have to be there before the gate closes is printed on your ticket.”
You don’t fly much I guess. If it is a connecting flight, then you have zero control over when you arrive at the airport. All sorts of things can delay flights, some under no one’s control, like the weather, and some due to the airline itself, like mechanical problems.
I’ve even seen airlines board everyone, then after learning the delay is going to be over an hour, they let everyone deplane and reboard again. There are always exceptions and if you fly often enough, you see them.