I just checked our FCOM. This pitch limit applies only to our most recent aircraft delivery. All others aircraft in the fleet don't have the same limit following a B+Y or G+B HYD system Fault.
The actual status message is:
FOR GA: MAX PITCH 15 DEG
when I first read it, I assume 15 degrees up only but it doesn't actually say that?
As to why? Hopefully someone better informed can enlighten us as the change with the latest computer versions.