And sure, you compared to Belize, an island country with much limited movement compared to the US.
Anti-science is not limited to anti-vaccines, it also encompasses all the public health measures, supposedly being a limitation on "freedom" and "bodily autonomy", claimed to be steppingstones to authoritarianism - all by people who want absolute 'freedumb', and all the benefits of living in a complex society but zero of the responsibilities of maintaining the complex society.
I will grant that the connection here is more tenuous than a herd of anti-vaxxers making a measles cluster and spreading it.
But the broad anti-science thrust both suppresses general public health measures, and in openly "anti-woke" states like Florida & Texas, the administrations actively undermine public health measures, even outlawing such measures, and preventing cities/counties from implementing their own.
Thus, it is no surprise to find that Texas and Florida are the locus of these infections, and to find that juxtaposed vs Belize successfully eradicating the disease.