What if the rewrite was intended to be competing product rather than a replacement for the existing one?

So many rewrites die as they attempts to reach parity and acceptance from users of the legacy version.

When a startup comes along and "disrupts" a product with their fancy new tech, they have basically done a rewrite without caring about the state of the legacy product. And then the incumbent often acquires them for a lot of money.

So, why not just do that whole process in-house?