Problem with rewrites is there is the terrible gap that opens up between the old stuff which goes stale quickly, and the new stuff which isn't ready for prime time. Cash-flow then dries up right as the amount of work needed is maximal. Death follows quickly.

Here they did not rewrite from scratch they developed a bridge that allowed them to keep moving forward as the world that the old software was based on disappeared. And now they are on the other side with a code-base that works and has been providing cash-flow the whole time.