I agree that in most cases it is the fault of an organization that problems were swept under the rug for far too long. There are cases were requirements changed

I agree that in most cases it is the fault of an organization that problems were swept under the rug for far too long. There are cases were requirements changed so much over the years that architecture of system would no longer support the business without massive cost or overhead. We have plenty of ideas on how to build new software: agile, TDD, DDD. It seems that there is no proven process for doing rewrites.