It is all very simple really.

Whatever we do, if we do not do it decisively, we just give the virus occasion to adapt.

population of hosts * selection pressure * number of generations * ability to pass material to next generation = adaptation

This is the same reason that the optimal strategy to use antibiotics is to avoid using them but when you need to, use a lot of it to make sure you kill completely whatever bacteria it is supposed to kill.

By not vaccinating thoroughly and keeping regime until the virus is largely gone we are giving it right conditions to keep adapting.

We are not going to get rid of this pandemic until everybody gets vaccinated or gets sick.