I recently experienced just this!

My flight boarded on the tarmac using air stairs from the front and back entrances. My seat was on row 15 of the 28 row plane.
Knowing little of the jet’s layout, and not receiving instructions about where to board, I guessed correctly when picking an entrance, but many people did not.
The entire middle third of the plane was a snarl of people crossing paths. With no clear direction of travel and only one aisle, it meant that people had to step into unfilled rows to allow’ oncoming passengers’ to pass. When overhead bins didn’t quite align with a seat row, people placed their bags nearest to where they entered, leading to the middle compartments being almost empty, and the ones around it being jam-packed. Moments later many passengers got up again and moved their bags to be in a more logical place - leading to delays for late boarders because the aisles were not clearing efficiently.

All-in-all, I couldn’t recommend it.

It perhaps could be more efficient with better communication and per-section boarding, but that means more announcements that could blend into background noise, and asking passengers to make more choices they could get wrong.

Here are my thoughts.

One part certainly is that you need to pay for more infrastructure, without a real benefit for the airline. Passenger boarding/deplaning is not the bottleneck for turnaround. Evidence: after boarding, you normally sit around for quite some time before the plane starts moving. You also need a flight attendant at each door, who is then bound up and cannot perform other duties.

With airstairs, it's different, because you often need buses, and you always need security personnel, and the faster you get all people off the apron, the better for everyone, so in that case, time is a factor.

Using airstairs in combination with the jetbridge introduces the security angle again, so you basically have the worst of both worlds, and have to pay for the jetbridge privilege and for security personnel. And if you don't separate the passengers by row properly, you won't even gain a lot, because more people have to pass each other in the aisles. As you have found out, passing through the door isn't actually the bottleneck, but stowing carry-on luggage and finding the right seat, and waiting for the aisle passenger to get up and let you get into your window seat.

P.S. I don't think it's a good idea to post this to two different communities. If you want to reach both, just post a short link to the discussion on the other community.

In the US I bet this is due to the airlines wanting you to feel the pain of sitting at the back of the plane. Whereas the people who buy first class tickets can get on and off without much discomfort and don’t need as much patience. Also probably 9/11 related security shit.

Having first class walk by everyone to board first is seen as an effective way to advertise first class.

They could also halve boarding speed by loading handicapped/parents with children first, then window seat, middle, aisle.

How is it twice as fast when you don't just have one person blocking the way until they unloaded... but instead multiple persons that are not even at their seat yet wanting to get past each other? That would only work if you separate the 2 groups to make sure they don't mix. So back side is back half, front is front half.

Also, note that the time it takes off usually also time they spend refueling etc., so it is inconvenient to you but not really for the Airline.