I've been traveling by air often lately and this question does arise from irate passengers but I always thought there was a simple explanation rather than thinking airline companies are actually stupid so here is that answer to a stupid question. Now it makes sense that first class enters first. Now if only the boarding groups where for window passengers first, then aisle seating

Why don’t airlines board starting with seats at the back of the plane forward?

I’m an airline pilot and although I understand the other answers hold some efficiency or economical benefit there is a much simpler reason we don’t board from the back first…

It’s to do with balance. The plane has its wheels in a triangular shape. The nose wheel At the front and the main landing gear which is at the middle of the aircraft under the wings… so the rear of the aircraft is balancing and has no support beneath it. So if we board the back first we would risk ‘tipping’ the plane like a seesaw and its nose will be in the air. It happens a lot more than you think, google some photos of a plane that has tipped. It’s even nearly happened to me. When using an air bridge, ie only disembarking through the front door, and people in the back are slow to get their stuff together, the plane can become aft heavy and the nose wheel extends fully in its strut to the point there is no weight on it. So sometimes as a passenger you may be asked to wait at the front for a little while before the cabin crew allow you off, this is to add some weight to the front and stop the tail hitting the floor. Planes that can only board at the rear, some ATR’s for example, and also some cargo aircraft have a stick/structure that ground crew place under the plane to basically prop the tail up from the ground as it is being boarded. But large jet airliners don’t have this.