i can’t tell if you’re asking in earnest or not, but the joke is rooted in subversion of expectations. puerto rico has 29 landfills, all of which are way over capacity, so trash is currently building up.

presumably he’s pointing out an actual problem on the island, while also poking fun at them in an offensive way.

the exact same joke has been pulled about england for the past 20 years, albeit without pointing out any sanitation issue.