Learning how to code is easy; a lot of teachers can do it. Learning how to debug is quite a bit harder. Learning how to debug someone else's code is a lot harder. But this is essential in being able to teach coding effectively (not debugging someone else's code as such, but being able to find the bug and steer the student into a way of finding it themselves).

Your proposition also assumes that you have enough Maths teachers, which Australia is certainly lacking (for the same reasons as OP)