I’m not sure what the percentage is of diver’s to non-divers overnighting on Cozumel is these days, but I would imagine it is not as high as some people on this board might think. The island’s target market is no longer divers and hasn’t been for some time. Although divers are most welcome and provide a large part (not largest part) of the tourist dollars that power the local economy, the government and the hotel investors would probably rather see more families and “big-spender” couples visit Cozumel. The island has an awful lot of low-end to medium quality accommodations already. The world’s other island resorts seem to be looking towards the high-end market for their future. Look at Palau. Used to be the name Palau was synonymous with diving. Now, they have decided the hordes of divers and Chinese tourists are wearing them down and they want to be more selective. Saw this article the other day: Jan. 10, 2017 – New legislation aimed at turning Palau into a luxury destination is to be put before the incoming congress which comes into power next week. The proposed law will restrict future investment to five-star hotel chains. The legislation is part of the president Tommy Remengesau's vision to reduce tourist numbers and increase tourist spending. President Remengesau says the new law, which he aims to have passed within the first 100 days of the new government's tenure, will include tax incentives for potential investors.
Other island destinations seem to be leaning in the same direction.
As far as the Westin and the Isla de Pasion hotels being far from the southern dive sites, I doubt that that even came up in the planning. I don’t believe they are aiming for divers. They are looking to sell to people who want a very nice room, excellent service, sandy beaches, clear water, and being in Mexico without “being in Mexico.”