There are thoughts that this factor wasn't a good idea when the NHS was set up. It seems to have come about/crept in as doctors were paid by the patient or people had to use a charity if they couldn't afford it.Wes Streeting has talked of bringing GPs and Dr surgeries fully into the NHS.
It also appears the NI was intended to cover the lot. We are way past that now. The NHS is run via the tax take.
I'm reminded of the chaos when the Tory privatised a group of tom nods to see if the disabled were disabled. Some were visited. I came across a soldier recently back from Iraq and not well. He was literally scared about the oncoming visit. Also a women who just about hobbled to a bus to attend an interview. They came up with a walking distance where people should be able to work.GPS are kind of privatised anyway.