Also, people like to sit next to people they know such as family. A column approach sounds more effective, but it would split up people traveling together.
Now friends sometimes end up in different seats, and you can probably get away with waiting somewhere, maybe on the plane itself to meet up, but if everyone is in the same boat it might be chaos to do that, and there is more incentive for airport staff to stop you.
Airports have waiting areas between arrival gate and passport control, probably precisely to let passengers traveling together catch up with each other. Even the worst possible airport would have a bathroom, and toilet entrances are implicitly a waiting (queueing) areas.
Unfortunately, introducing any sort of rigid structure and order into airplane disembarkation process sounds like an impossible task.