On really long flights, issues that are trivially ignorable at short distances (<5 hours) become more of an problem. In a lot of current coach seating on airlines, the biggest problem I run into sometimes is not where to place my legs, though that does require a lot of manuevering for anyone over 5′ 11″. It’s the question of elbows. On the aisle or the window, you have uncontested mastery over one side of your body, but the other is the unknown. The best part of flying with someone you know well is that you can generally dispense with the awkward unconscious struggle over territory and bodily contact and just go ahead and have your body sides touching.
On the London-Joberg leg this time, I was sitting next to an elbow aggressor, though, and that’s tough. The guy insisted on owning the entire real estate of his chair and a bit into mine as well. When you’re trying to sleep, having to clutch your right arm in order to keep it from colliding into the space already occupied by another person is pretty tough. (It didn’t help that Mr. Elbow also insisted on watching comedies all night on the in-flight entertainment and laughing at the top of his voice.) It may be that male awkwardness about body space and contact with other male bodies makes this more of a tension, I dunno. But the compression of space in both directions, between rows and between seats, makes flying distances a real agony.
Why are seats narrow? On a 777, only eight 18.5 inch wide seats can be fitted into a row and still allow room for aisles, but nine 17.5 inch seats will fit. A 12.5% increase in capacity! Other airplanes, similar calculations. So even airlines which provide greater seat pitch than BA’s miserly 31 inches keep the 17.5 inch width.
BA, by the way, in their “a step above steerage” class, does provide 18.5 inch wide seats (and 38 inch pitch), but charges extra for them.
Airline economics: always the low price.
You complained below about the lack of layover facilities at airports. Partly that’s the result of airport architects ignoring the problem. The majority of trips, even now (but more so when most airport terminals were designed), are direct. To optimize for them, you need to make ground transport to check-in to gate and gate to baggage claim to ground transport as short and unencumbered as possible, while fitting in as many gates as possible. This is hard enough, without worrying about layovers (or gate to gate). But no-one’s fixed it because travellers aren’t the airport’s customers, airlines are. And airlines like the lack of layover facilities. That lack allows them to sell their lounges, either as a frequent flier perk or for a subscription.
Airline economics: make the cheapest option uncomfortable, then sell relief.