Lack of inter-generational knowledge transfer doesn't cut it. Most of the people who rolled this stuff are still alive. And as for the whipper-snappers: people don't get very far writing programming languages/video games/operating systems without knowing their stuff.
The real boogeyman is feature combinatorics. When making a tightly-integrated product (which people tend to expect these days), adding "just" one new feature (when you already have 100 of them) means touching several (if not all 100) things.
Take OpenBSD for example: When you have a volunteer project by nerds for nerds, prioritizing getting it right (over having the fastest benchmark or feature-parity with X) is still manageable.
Bring that into a market scenario (where buyers have a vague to non-existent understanding of what they're even buying), and we get what we get. Software companies live and die by benchmark and feature parity, and as long as it crashes and frustrates less than the other guy's product, the cash will keep coming in.