On a recent flight, an airline employee (either gate agent or flight attendant) who had just stepped out of the plane told my family that there was no more room in the overhead compartments, and we needed to gate-check our bags. I asked if we could keep just one, but was told it was completely full. So we checked them, after stuffing everything we absolutely needed into my son's backpack and wife's purse.
As soon as we got onto the plane, we realized that there were plenty of empty overhead spaces, especially near the back where we were seated. The first employee had outright lied to us. I mentioned this to a flight attendant who said that the reason was just time based - once we got close enough to takeoff, they automatically started gate-checking carry-ons. We then noticed that passengers behind us in line still had their carry ons. So that didn't seem accurate either. So a 3rd attendant told us that it was solely weight based - the airplanes had to balance the amount of weight above and below the passenger compartment.
Is this accurate? Do airlines gate-check carry-ons because there is too much weight up top or none on the bottom? If so, how do they choose which and how many bags to check? If not, what reasons other than room would cause the airline to gate-check bags?