When people enter an airport they are funneled through a structured area as they go through the security checkpoint; the queue of humans is cordoned off with stanchions and employees keeping things relatively organized.
Then those same people get to the gate for their flight, and the onus to maintain order is left up to those same people who couldn't be trusted minutes earlier. The waiting area by the gate has a counter behind which the employees make announcements about which group gets to board, and there's a bunch of chairs where the pending passengers sit. Beyond that, there's no structure imposed on the space, so when the staff starts announcing who gets to board, people coming from multiple directions to that point of entry at the gate have to queue up with nothing but the patience of some and the pushiness of others to guide them.
However, what may be most befuddling is those who form a perimeter around the area where the line to board forms. The announcement about which group can board is made, and these people who are not in that group stand up and congregate near that spot. While they clearly seek to get on the plane as soon as possible, the way they assemble into an unintentional wall makes it such that they are blocking those who are allowed to board to getting to the gate, and thus only delaying the time it takes for those predecessors to get processed and allow the staff to announce that those on the periphery can do what they impatiently await.
I'm not sure how people go from structurally incapable at security to organizationally empowered at the gate. Clearly airport designers give people too much credit... or not enough.
No, too much.
Bring on the stanchions by the gate! If that doesn't work, we'll move on to an electrified fence...