Oahu has about 1 million people, Maui has about 170,000 not including tourists. The islands are not far apart in size. Steve-o is right , the north shore and some other areas are still very nice and beaches are public in Hawaii which saves it, otherwise they would be mostly closed. Traffic is terrible pretty much everywhere on Oahu. A famous bay that was being killed with visitors (Hanauma Bay) was finally put on some visitor restrictions so the reef could come back and it's doing better. Starting in October, they can't sell sunscreen here on Maui with certain chemicals that tend to kill the reefs here, which are suffering like they all are.
Oh, and I know of one beach that is private, it's a property about 10 miles from where I live and Jeff Bezos just bought it.
All in all, I'd still rather be here than on Oahu, or in Hawaii for that matter, best weather on the planet and property taxes are low.