Why can't airlines devise a better boarding process?

Airlines routinely assign economy-class passengers a boarding zone at the check-in desk.

According to this system, passengers seated at the rear of the aircraft board first, those at the front board last, but it doesn't work.

Test scenarios have shown that this is the slowest system of boarding.

The fastest way to get all passengers into their seats is known as WilMA.

Passengers in window seats board first, those in aisle seats board last with middle-seat flyers boarding in between.

That's problematic since it splits families. Nor does it solve the problem of passengers who block aisles, trying to cram their oversize bag into the overhead bin.

Some researchers have suggested a complicated boarding system that sees passengers with the most carry-on luggage assigned to window seats and boarding first, but the real problem is us.

As it is, passengers will routinely stampede the gate as soon as boarding commences, disregarding their assigned boarding order, and airline staff are reluctant to impose the rules.  

Changing to a system that gets passengers seated quicker is not hard, but changing human behaviour is a lot more complicated.