I thought comfort aboard is what the operator wants to provide hence the outside bears very little reference on what is inside. I flew on an A320 that was unusual tight for my normal airline so I asked the cabin crew and sure enough they were leased from an ailing competitor.
I guess to some extent, though the economics of that is going to be made easier / harder by the dimensions of the aircraft. Also there's not a lot they can do about the noisiness of a given aircraft.
Interesting that your regular airline's norm was for a roomier cabin, and their
ailing competitor crammed passengers in. Some sort of lesson there?
From reading other threads here it seems that Boeing have made it harder with the 787 being a touch too narrow, for example. They're also talking about somehow being able to cram in an extra seat in a row in 777x...
In contrast, and if Emirates are anything to go by, it seems that Airbus have managed to make the A380 reasonably economic to fly, a generously comfortable proposition for economy class, quiet, reliable, and big enough to accommodate crazily large things like The Residence and make it one of the most profitable seats one can buy a ticket for.
There's also the simple matter of being able to carry more passengers in one go than anything else in the sky. Having the biggest plane and somehow contriving to fill it up every flight whilst your competitors are flying 777s means that you have a larger share of the market. Market share matters quite a lot.
There is talk about trying to squeeze in an extra seat per row on the A380, but I think that would be a mistake. Emirates have publicly said they want an A380neo, which would be a way of getting better economics without having to squeeze in that extra seat. A stretch would be very appealing too I imagine.