Hospital car parks around here tend to be rammed full even with the current charging regime. Given that many hospitals have prime central sites, you cannot just offer free parking - there is no free parking in the surrounding area, so it would be an invitation for commuters, shoppers and others to park for free.
You would need to work on the supermarket principle for validated parking. But then you run the risk of clinical staff having to enforce parking terms - making judgements as to who is entitled. I suppose you could draw the line at people attending appointments and close relatives visiting - how close is close though?
Through the joys of parenthood I have experienced many of the NHS's finest venues. And most of them have less parking than demand.
It is a costed measure and it is a populist gesture. But they need to start weaving a narrative. It still feels like some random gestures rather than a coherent offering.