It's really not about politics, the vaccine simply didn't roll out fast enough to the entire population of the planet. What happened in the US is actually not that relevant as the US is only about 5% of the population of the planet, i.e. it's only 5% responsible for mutations, as the rate of mutations is proportional to the size of the susceptible population.

This is actually a "shortcoming" of tech. In quotes because the tech of the mRNA vaccines is actually stunning, but it just wasn't fast enough to test and manufacture (development was pretty much instant, the vaccines were ready in January 2020).