If Puerto Rico were to become a independent nation, I would have trouble seeing them being "charged" for land prior to their departure. So why would Louisiana?
Puerto Rico has sufficiently different circumstances to not make this an apples to apples comparison. They already owned the land when they were independent of the United States. There was no state of Louisiana independent of the United States and the overwhelming majority of people who live there are descendants of US settlers.
Hawaii or Texas might be arguably closer to Puerto Rico than Louisiana, but there's still the difference that Puerto Rico is not integrated so there's no disruption from severing it.