In a large enough system a full rewrite becomes impractical anyway, because the team is sized to incrementally grow not replace whole cloth. The team simply isn

In a large enough system a full rewrite becomes impractical anyway, because the team is sized to incrementally grow not replace whole cloth. The team simply isn’t capable of rewriting the whole codebase in one big bang release in anything less than years. You can bring up a larger team for the rebuild but that introduces its own risk, or you can leave customers out in the cold for years, like netscape did. Continuous rewrites are the only way to handle that kind of system, just like in a large enough city just to keep up with natural decay it becomes necessary to always have construction and road works projects going on.