OWB on the sea are actually illegal in Thailand
construction need to keep a certain distance to the shore. All beaches in general are meant to be public in Thailand
that many hotels or private owners use excessively land at the shore without facing legal problems is another topic, but if they built OWB on the sea, it would probably be too obvious and get attention in the social media so that authorities would have to act (there were some cases in the past)

I have seen OWB in nearby Malaysia, for example on Langkawi