I disagree that the cause of the problem is complexity stemming from size, and propose that the real issue is the industry's poor history of efficient documentation. Processes to efficiently create and read documents that describe large systems are rarely in place at most of the places I've seen. That's probably the biggest barrier to contributing code to old framework Y. It's just easier to develop framework Z. I agree with you that some things can be designed to reduce complexity, but ironically whenever something like this happens, someone from an older product will glean ideas of the new one and port some of those concepts over (potentially further proving that the big problem is the lack of resources for understanding)