As for Okinawa that seems to depend on the island. When I was there some years ago, many beaches on the smaller islands were covered in trash (mostly of Western origin – one could often still decipher the letters on e.g. beer and shampoo bottles).
Personally, I'm not surprised Japan has a plastic waste problem, the shops and manufacturers here are addicted to plastic, and the culture is one of appearances above truth so I'm not surprised to hear about the differing levels of care dependent on whether tourists frequent a place.
I've also lived in other parts of Asia and I've seen some shocking things to do with waste. India was the worst. As another comment mentions, it's probably best that developed nations export knowledge and attitude towards waste, not just waste.