Some of the other comments refer to rewrites where the intention was to expand scope / technology / scale / etc. The Healthcare.gov rewrite was simply to make a

Some of the other comments refer to rewrites where the intention was to expand scope / technology / scale / etc. The Healthcare.gov rewrite was simply to make a functional system. If you have a system that does A, it is absolutely easy (relative to greenfield) to rewrite another system to do A. The problem is that most rewrites don't just set out to do A, but to also incorporate B, C, D and E, with an easy framework that enables F, G and H, and...