Same reason they don't use full size firewire ports, big corperate half assed attempts to keep the pro out of prosumer.
Unless your willing to spend 4+ times the cost of the HVX you will never get what you want or need regardless of how easy and it would be to impliment.
They tease us and they love doing it, sony more so than pana but it's always been the case.
One workaround would be to generate color bars with tone in your NLE and save the clip on the HVX. If your NLE doesn't have that feature or you don't know how to do it, I can provide such a file, just let me know the format you need.
Of course once you format the P2 card you're back to the same problem, but it might be useful when you first set up, and you can always put the color bar clip back onto a P2 card if you need it again.