Labour won't attack on this because they know it might have happened to them just as easily, whereas it fits the Tory narrative that "the NHS is useless and should be privatised" with almost no spin.
Most of my local Tories know that any kind of direct assault on the NHS would result in instant annihilation at the next election.
There are more subtle methods of course including outrageously broken internal market management restructures (Stafford Hospital Trust, 'fund holding GPs' in the time of Thatcher) and the like.