What I've found is that often a flight will take the same gate as it took yesterday, and failing that a nearby one. I think people like to be near their gate to feel safer about missing the flight. You mightn't know know the exact date, but since airports won't even give you the general area.
Also I don't believe your efficiency story, there are plenty of cases where it's possible to know the gate ahead of time, and plenty of reasons for airports not to want people congregating at the gate as soon as they get airside.
> there are plenty of cases where it's possible to know the gate ahead of time
exactly, sometimes even flight radar tells you the gate, but the main displays in the airport will tell you the gate number only 30 minutes before: Istanbul (IST) is my main reference here: what I do is I just go to any personnel and gently ask for the gate for my flight telling them I need to sit down and rest: they quickly check and tell me.
I have no proof, but I do believe that those 30 mins only advance notification are planned so not to have me sitting down in a comfortable chair for hours not spending money.
My local airport only has 8 gates for american airlines. They are constantly landing without a gate. Sometimes you get to file your gate early, sometimes you don't. Not having a gate doesn't prevent you from filing an IFR flight plan and getting to your destination. It just means you might sit on the tarmack because you are not flying into a hub for your airline
Also I don't believe your efficiency story, there are plenty of cases where it's possible to know the gate ahead of time, and plenty of reasons for airports not to want people congregating at the gate as soon as they get airside.