because with the variants circulating, vaccination is not a black-white all clear vs. someone who hasn't been vaccinated.
further:
acknowledged high-rates of asymptomatic transfer mean that many refused travel/access will have more protection that the 5+ percent for which the vaccines do not work.
why not also ban that 5+ percent in that the vaccines do not work for them? in the case of the SA variant it is higher than 5%.
why not ban under 16's (for now)?
the dividing line is not science. it is drawn so as to pressure people to get vaccinated. it is drawn to make it palatable to those who fall on the "have vaccinated" side of things.
finally transmission
rates are still high and we know Asymptomatic Coronavirus Patients Can Still Develop Lung Damage | Global Biodefense etc so allowing vaccinated to mix opens them up to asymptomatic damage.
(please try to resist the urge to imply refutation by selective response).