Because "build atop a crumbling foundation" has demonstrated time and again to be, by far, the most successful way to accomplish anything in computing?I can't imagine where that sort of conclusion comes from. Building on a crumbling foundation seems to be just about the most proven, reliable way to ensure your software project won't survive more than a short time without needing serious effort just to maintain it and/or a big rewrite.
Much of the world still runs on C, a language that was created long before many of us here were born. Other languages have risen, peaked, and fallen into relative obscurity since then, yet C endures, because for all its faults, it is simple and predictable, the epitome of a sound foundation.
Large amounts of COBOL is still driving back office systems in large organisations. The cost of hiring people with the skills to maintain them is probably horrific, but those systems are still there, doing their jobs decades later.
You can still run applications from nearly 20 years ago on Windows today, in no small part because of Microsoft's persistent focus on compatibility and keeping the basics reliable over that time. Similar stories can be told in *nix world.
What major accomplishments in computing that have been built atop crumbling foundations can claim anything even close to the scale of success of these examples? You surely can't be talking about the move fast and break stuff philosophy that seems to drive everything at trendy software shops like Facebook and Google, or the kind of MVP/lean start-up hype we hear about ad nauseam on HN and the lasts-just-long-enough-to-exit web apps that result.