I am somewhat talking through my todger here but it's a fascinating issue.
I don't think it's because they are cheap. After all things which are desirable (like diesel VW Golfs) usually sell at a premium. My theory is the 737 was optimised for reliable shortish sector turnarounds, maybe at the expense of a few other things like economy. The Southwest model rests more than anything on doing a series of sectors with one plane without a hitch. Or perhaps if there is a hitch, then ease of support is vital.
Possible the A320 could show itself to be as
repeatable but it takes time to get a reputation.
As I say - just a theory.
