When selecting airplanes, seat counts are not as much of a factor as you would think
Trip costs tell an airline how "small" an aircraft is. If you waved a magic wand and got a 747 with the trip cost of a 737, that plane could be used on any 737 route that has a airport that can take its physical size at both ends. Doesn't matter if 300 seats go empty, it cost the same to go from A to B. For highest accuracy you throw into the trip cost, the portion of total lifetime MX
, acquisition cost, etc. So a plane that flys for 20 years before being scrapped, costs 182.5 Million, and flys 1 trip a day would have a cost per trip of 182.5/(365*1*20) or .03million a trip. Get 2 trips a day and each trip costs .015million for its "share" of the initial price. (its alot more complex with the time value of money, but we are not actually buying planes, just armchair arguing). So If your total price of plane X per trip in your usage is less than plane Z, you will ah, not care too much if plane X flys around with alot of empty seats. Rarely happens in reality, but it can. The 787 will be one to do this to ALOT of aircraft.
Revenue potential is another metric to look at. Its what is the plane capable of generating cash. This isn't a simple Seats X seat price calculation. You have demand curves, of which vary given a route, time of day, day of week, season, etc. You also have cargo concerns with its own demand curve though with less complexity. You also have interestingly enough the value of the aircraft frame itself. After all if you can make more money leasing it to Jimbob airlines than you can on your available routes, leasing it might be a better option. Ryanair also supposedly makes some cash by taking new build frames and slinging used ones to airlines that can't get a deep discount or need the frame asap.
Risk is also a factor. Operational risk largely boils down to trip cost, though dispatch rates, high insurance rates, uncertainty about lifetime performance, etc are added in for a more complete risk picture. This is one thing that even if you won every lottery on the planet that would stop you from being able to compete with Boeing or Airbus as a new plane maker. The risk of taking one of your unknown aircraft into your fleet is very high compared to the known makers. Even the Russians have an advantage as even if you as the buyer think their planes are puppy poo in airplane form, its a known risk, and can be evaluated.
Opportunity cost. The "cost" in REAL TERMS. Taking a free sample from a vendor has an opportunity cost. It costs you time/effort/whatever to get that sample of said product even if you don't pay any money for it. So when acquiring planes, you have to look at the total cost to your airline to get a certain airframe. Lets say you are WN
. Buying A380 has stupid insane opportunity costs since they would have to spend not only the money on the planes, MX
training, pilot training, airport improvements, etc. but they would also have to spend the time and money to figure out how to not lose their shirt operating them. Trying to find routes for A380 would cost them dear in time/resources better spend on finding new places to kick 737 flights to. So here is a clear case where even if you could make a case for WN
owning A380 based on CASM, RASM, certain routes, whatever... you won't ever see it happen because it costs too damn much in opportunity costs.
So right now the A380 has a couple problems, High trip costs. Means that there is few routes that can take its "weight". the early adopters with their penalty payments and low initial cost will see a big benefit as the per-trip share of the initial price is lower. Revenue potential is also a concern. Its passenger only, with no cargo to back it up. So off seasons, market slumps, competition can all turn a cash cow into a rotting corpse in a hurry as the passenger revenue falls off a cliff and costs remain high.
The 748 has some issues too. Risk is one of them. Do you pay a fairly high price for a 748 when if you wait a year you might pick up a A380 for less per frame due to Airbus potentially having to sell frames a heavy discounts because thats what the economics on their side says is best for them. (variable cost to produce A380 decides the true minimum price)
Risk is also higher than just grabbing a few more 777 frames and seeing what the 787, A350, Y3 bring to the plate.
Opportunity costs for the 748 is mixed. Can't steal A380 some orders even with fairly dramatic price/performance/whatever benefits since the cost to switch to the 748 in opportunity costs is way too high. (aka why the 748 would have to walk on water before some airlines cancel). Also hurting is many airlines that would love a 748, also need 777 or smaller aircraft. With limited resources, the opportunity cost of the 748 may simply be too high over getting the midsized fleets sorted out on the current time/money/manpower budgets available to the airline
Now many people fall into the trap of shopping based on some artificial size constraint because its easy. Its easy to assume that the A380 has no competition because the 748 is 80 seats away in capacity, yet only sloppy CEO's would get that intellectually lazy. A bad CEO instead of a terrible one would today evaluate the 748 and the A380 at a minimum. The good ones would also look at all the mid size aircraft. The best ones look at everything including sitting on their hands and ordering nothing. For true evaluations, everything competes with everything.
(as a side note I will just assume that people will get upset that I made the statement that the A380 might have to be sold at bare minimum prices to get sales. This is in fact my belief, mostly supported by the notion that has a very self-fufilling prophecy aspect to it. That is that if Airlines refuse to buy because they assume that the deepest discounts possible are only a bit of waiting away, then in fact that is what Airbus will be forced to do on their side given no incoming orders with reasonable margins. I've seen it happen in a good many industries this way, Where the customers assume sales failure and thus cheap items to try and just put a little back in the bank, and thus... it is a sales failure because everyone was waiting to buy.)