This is the famous trap that Joel on Software talked about in a blog post long time ago.

If you do a rewrite you essentially put everything else on halt while rewriting.

If you keep doing feature dev on the old while another "tiger team" is doing the rewrite port then these two teams are essentially in a race against each other and the port will likely never catch up. (Depending on relative velocities)

Maybe they think that they can to this LLM assisted tools in a big bang approach quickly and then continue from there without spending too much time on it.