Can't speak for the US but the extra cost buys you reliability and convenience. I can be late to checkin and assuming the gate's still open I'll make it out on time. Try doing that on a budget carrier.

But how does it compare to SW? I’m trying to not sound like a shill, but do you have free cancels and changes up to 10 minutes before boarding, kiosk check in and curbside baggage check? Super easy to use website and app that doesn’t hide costs and also makes it easy to change flights and see the exact price difference and actually refunds you money if the new flight is cheaper?

With SW I’d be completely comfortable booking a flight 6 months out that I had a 25% chance of actually taking.

I’m trying to actually understand why the major airlines have customers.

Delta gets most of my business travel. I live near a second tier Delta hub (Boston) and all of my recurring business trips in the US are non-stop (most) or one-stop (a minority).

I can book my trip, select my seat (none of the trying to check in 23h59m59s998ms ahead, only to find you got A12 anyway and then 42 people had some reason to have priority boarding including the in-flight miracles where someone needs a wheelchair to board early, but walks off on their own), and if there are irregular ops challenges, Delta likely has 2-5 other similar flights in their network.

We fly SWA sometimes for personal travel and I can say “it’s better than Spirit, but I prefer Delta.” (We fly Delta even when it’s our own money, unless SWA has a non-stop and Delta doesn’t.)

Isn't SW the airline that completely fucked almost all of its customers nationwide last holiday season because they don't have a hub and spoke network? That is probably a good enough reason not to rely on them at this point.