The question in the title is very very easy to answer. The political reason that natural immunity “doesn’t count” indeed is not directly about medical reality.

The question in the title is very very easy to answer. The political reason that natural immunity “doesn’t count” indeed is not directly about medical reality. To say things are political is almost an insult these days—I don’t mean it that way at all. But policy has medical implications, and so politics is part of it. This policy-decision is being made because there have been political movements since early on to do variations on “Let 'er rip,” that is, to allow COVID-19 to run rampant until a herd immunity develops, while maybe implementing decontamination procedures in nursing homes instead or so. The most notable statement to this effect was the Great Barrington Declaration but of course there have been smaller ones that hit wider spread. Policy needs to factor in things like the huge early oppositions to shutdowns, the huge oppositions to masking despite it being absurdly effective for how cheap it is... there remain very strong political forces in this divided country which overlook the significance of younger people with COVID flooding the emergency rooms and overtaxing our limited health workers (NYT today reports that in the US South, they are at this level right now), and the death that can come from this, simply because the danger for young people is usually considerably smaller when those hospitals are operating normally. (See India for a cautionary tale, there.) Given this political reality, ‘vaccinate everyone’ is a political countermeasure meant to create a potential-energy-barrier to lying. It’s not medical advice, it’s public policy. Lying to say ‘Yeah I was COVID-exposed but it wasn’t bad enough to go to the hospital’ is very very cheap. Forging a CDC vaccination card takes a couple hours of time right now and opens you up to some fraud risks—it’s not a huge cost but if it’s higher than the cost of just going and getting vaccinated, there is a hope that vaccination will win out.