What you don't seem to know is the number of transactions the low end custom (one-off) builders are actually involved with. For all you economics knowledge you should be aware that a group representing a fraction of one percent of market share isn't going to move the needle.
they don't need to
it is my choice
I prefer to pay towards the lower end of the custom spectrum as opposed to pay at the top of the fender spectrum
your choice may vary
good luck to you