The answer is pretty simple - the moment authorities start saying "well, natural immunity is probably just as good as vaccination, we'll accept that as equal to vaccination for passport purposes", a huge segment of the population who's on the fence about getting the vaccine might just opt to wait until they're infected naturally, or, even worse, get infected purposefully (EG, chicken pox parties). Which leads to more deaths and outbreaks.
In a perfect world, everyone would understand that getting the vaccine is the appropriate choice of action and we could accept natural immunity from people who were infected before vaccines were available - but unfortunately we're forced into playing these weird games where authorities have to try to incentivize people who aren't behaving rationally - which in turn leads to further distrust from people on the fence.
In a perfect world, everyone would understand that getting the vaccine is the appropriate choice of action and we could accept natural immunity from people who were infected before vaccines were available - but unfortunately we're forced into playing these weird games where authorities have to try to incentivize people who aren't behaving rationally - which in turn leads to further distrust from people on the fence.