I thought the route still hadn’t been finalised for the northern leg of HS2. Also high speed means you’re less flexible, as you need to go in a straighter line than normal rail.
I agree that it seems unlikely that the extra effort to complete the northern leg of HS2 would be greater than that of starting from scratch, but I’ve been surprised before.
This is for trains… My guess is that it’s for 20-30 year olds that commute by rail