My understanding is that historically, the vote has been almost 50/50, but that there have been issues with the question that have thrown up doubts about the validity of the referendum conclusions. Stuff like giving the options of statehood or territory, but not independence, etc. Even the one you linked says that only around half of the population responded and over 200,000 ballots were thrown out for either being blank or invalid.

I had thought that a significant portion of the population had been in favor of independence, especially since we came in and basically destroyed their economy. They had been one of the largest manufacturers of pharmaceuticals in the world before the US, and now I think their biggest industry is tourism, which, as someone who has lived in a tourist town for decades, is not conducive to a healthy economy.