Why does my freehub body have such shallow lockring threads? My new freehub body (right) has much shallower threads than my old one (left). The threads are so shallow that I cannot properly install the cassette lockring.

They are both for Campagnolo 9/10/11 speed. I am using the standard lockring that came with my Campagnolo 11 speed cassette.
How can I fix this?
The right hand one appears to have been assembled incorrectly. You may be able to fix this by pushing the bearing home with a suitable press but you'd be better off referring the problem back to the supplier of the part who will likely exchange it.
Which of the two routes you take depends very much on where the part came from and how you want to spend your time. It is very frustrating when new parts arrive in this condition!