For the same reason the government has been pushing through this NHS database system, is exactly the same reason that the NHS is now a target.
It is tantamount to using the Red Cross for military operations. Medical systems were often thought of as no go areas for crackers, now they are the focus, and that has created quite a leap for the NHS IT support system - they will have seen very little cracker activity and then suddenly seen it spike high (if they even bother monitoring).
Enough concern has been expressed over the keeping of medical data on digital systems connected in anyway to the Net, that whoever is ultimately responsible for this storage is now guilty of gross misconduct, and a party to identification theft. I would go so far as to say anyone involved in the development, deployment and operation of the NHS database system are also guilty, but unfortunately only a few heads tend to roll even when the incompetence is en masse.
The sooner we replace medical resources with robotics the better. Time to drop the redundant human element altogether from doctoring. There is no reason whatsoever to keep medical data on most people, the urge to keep data is a human one of simple noseyness and control.
The BBC have reported this story a couple of days ago, so there is little doubt this is not a legitimate story.