The bad thing about a brain is it's inside a skull. Makes it hard to do adjustments.
If you're designing something new, like hands, you need more robust neural pathways. Then it's easy to add an access point between the ulna and radius.
The hard part was giving you a proper ulna and radius in the first place. Bear D.N.A. probably made you clumsy as a puppy, but I think you'll agree that having wrists when you grew up was worth it.