Pretty simple, really: People are more willing to pay money to reduce construction time.
You see the same thing in a lot of hobby fields. Thirty years ago, you either built an RC airplane from plans or from a kit where you still had to glue all the ribs, spars, stringers, bulkheads, etc. Nowadays, most are sold ready-to-fly or Almost ready-to-fly (ARF). People are less interested in spending time constructing.
Same thing for the full-scale airplanes.
Ron Wanttaja