5 years ago, quickly contained? Noteworthy, sure, but unrelated to this article.
The question you should be asking is, "why are measles able to spread through US populations" regardless of origin? From the article:
Jha said that the dramatic rise in measles cases on Kennedy’s watch was not coincidental. “The administration has not done enough to promote vaccines. It has not done enough to highlight the harms that come from measles.”
Honestly, I'm surprised RFK Jr. changed his position at all. Some parents of children who die of measles double down on their decision not to vaccinate.