Whoa there, armchair CEO dayflier.
Many airlines are getting along great with planes that are far older than 15. Southwest, Northwest, and American come to mind. Southwest is flying some great old 737-2H4's, Northwest has their reliable niners, and American is flying some MD
-80s that have broken the 20 year mark. Does it make sense to spend forty million to replace a plane that is working fine? No, it does not, especially when you are in BK court- and I don't mean burger king anymore.
How would they get rid of the entire 737 and 757 fleets? Uh, there aren't enough 320s in the fleet to do all the flying, AND
they don't meet the needs.
Have you realized that there are things the 320 series planes cannot do? They need 757s for that.
And like you said- it's not about seats anymore- the 777 is too big for almost all of their routes- hence they are parking them in the desert. That's why they have... You guessed it, the 767.
Fleet simplification would NOT turn United into a profit machine overnight.
Rumor had it that the 735s were ALL
going to go. Which doesn't make sense to me- they are efficient airplanes (just ask Southwest- they like them a lot!), and they don't have an Airbus equivalent in the fleet. The 318 would be an okay replacement (though not perfect, due to different design intentions) but it doesn't matter, because UA
doesn't HAVE the 318.