Literally nobody said the COVID vaccine would last forever.
You're assuming the reason for the booster is for the dwindling effectiveness over 6 months. However, there are those making a case that after the 3rd dose you have a better defense against delta vs. 2 even if the 2 was recent.. which means we may soon require a 3 dose regime in order to be considered vaccinated and it may go to 4, 5...
Just curious how many people left do you know that definitely did not covid (via antibody testing) and got the vaccine, were exposed to covid, and did not get covid?