New airliner types are actually pretty uncommon. New models of existing types happen more often, and are typically incremental improvements on the basic design, and usually do not rebuild/redesign the wings or other major flight-oriented components of the airframe.

Consider that in the past 15 years only three new types (Airbus A380 and A350, and Boeing 787) have entered service from the two major manufacturers, while the same time period has seen nine new models of pre-existing types from those manufacturers (the A320neo, the high-takeoff-weight variant of the A330, the 737-900, 747-8, 777-200LR, 777-300ER and the 787-9).

This isn't software development. Why reinvent the wheel?

Same could be said for CNC machining.