Airlines started charging for checked bags so everyone started bringing massive carry-on bags. If you board last, there is no room for your bag. So it's a "perk" to get on first as an economy passenger. Boarding order for economy is usually 1. Frequent fliers with status giving them priority boarding, who also get to choose their seat and pick as close to the front as they can, 2. Back to front in "zones".
I'd also add, I've seen some more sophisticated theoretical boarding strategies, but passengers have trouble even understanding zones, there's no chance of boarding alternate rows or whatever working in practice.
I'd also add, I've seen some more sophisticated theoretical boarding strategies, but passengers have trouble even understanding zones, there's no chance of boarding alternate rows or whatever working in practice.