The science says get vaccinated. It is not required to be vaccinated to deliver goods domestically because that would mean imposing the vaccine on citizens of their own respective countries, which is a can of worms neither government wants to open.

But requiring foreign visitors to have certain vaccines is much less politically fraught. If you don't like it, tough, you don't get to enter said country.

Asking what is the science behind these decisions is being disingenuous and you know that. Please stop.