It's a bit confused, much like Americans wanting the government to get out of their Medicare, but Brexit support was, in part, due to the decline of public services in much of England and the belief that "those people" were taking all the money. Immigrants, Europe, unnamed other undeserving people, etc. The extra money for NHS was always transparently bullshit, but it was bullshit that some
people believed.
Theresa May has told the head of the NHS that it will get no extra money despite rapidly escalating problems that led to warnings this week that hospitals are close to breaking point.