Why is that? I don't know a lot about re-writing a code base in a different language, but I doubt the time/effort required for the re-write is the only conside

Why is that? I don't know a lot about re-writing a code base in a different language, but I doubt the time/effort required for the re-write is the only consideration. You're not just replacing the source, you're replacing the entire development process. Tools, processes, talent, stack.