Nobody ever said rewrites are always a bad idea. You just made that up. It has been done successfully many times, with many more happening (e.g. TypeScript compiler rewrite).

What matters is how the project is planned and implemented.

Typically, complete rewrites that halt all feature development and fail to achieve feature parity is a recipe for disaster. On the other hand, balancing the work for feature/regular maintenance and rewrite and gradually achieving feature parity before rolling things out has worked well.