Measles was mostly benign before some money making corporation told you otherwise: https://youtu.be/d3hP84qQz4o
Measles is highly, highly, absurdly contagious and you spread the disease for up to four days before symptoms appear.
Therefore, even if its "mostly benign" in healthy individuals, it has a very high potential to infect immunocompromised individuals, so it's a public health concern.
Some diseases are more acute than others, but if we can eliminate even non-acute diseases, why wouldn't we? And to be clear: we know we can eliminate measles because we already did it once.
They're really an outlier there, huh?