I'm surprised this didn't happen sooner. Based on the first result [1] searching "percent of americans vaccinated for covid": it's 79%. So flipping perspective: The unvaccinated 21% made up 42% of deaths. It's disappointing that even a hint of this context is missing from the article.
It would have happened sooner if vaccine acceptance were higher among the older and/or lower among the younger. The same thing happens every flu season: Older people get vaccinated but some still die, while the 20-year-olds don't die from a flu no matter what.