The molecular clock is a wonderful tool. It allows us to put a date on the emergence of new species, or in the case of viruses, new viral lineages.
Luckily, we have the public record to tell us when variants were first detected. The Delta variant, for example, was first detected in late 2020, long before any COVID-19 vaccination program.
That did not stop vaccine zealots from launching a half-hearted attempt to blame the "Unvaccinated" as the source of new variants.
Since we know variants emerged before there were "Vaccinated" or "Unvaccinated" categories of people, the emergence and spread of new variants requires no special explanation. Evolution happens. But there are a few factors that are in place that are helping the emergence of new variants.