I mean they probably do somewhere, but not in any of the hotel gift shops, convenience stores, pharmacies, or dive shops where I looked.

Well, you did say "anywhere in the country".

Shouldn't it be the only sunscreen they sell there? It's in their best interest

Have you compared the amazon reviews between "normal" and "reef safe" sunscreens? "reef safe" stuff has poor reviews almost across the board, where as "normal" sunscreens often have excellent reviews.

Are you sure nanoparticles are reef safe? These particles break down too.

They do? Into what?

In any case, the issue is with other types of biologically active sunscreen ingredients.

https://cdhc.noaa.gov/_docs/Site%20Bulletin_Sunscreen_final....

One paper I read ages ago suggested these nanoparticles had similar behaviors subdermal as asbestos but drew no conclusions if they're carcinogenic. Then there's a few references floating about that I can't verify the veracity of that zinc oxide nanoparticles exposed to UV breakdown into free radicals.

Google search: zinc oxide nanoparticles free radical

The larger particle, and thus opaque versions of these sunblocks seem to behave as you'd expect, they stay on the surface of the skin pretty much entirely wash off and don't interact with the environment. But they're visible light opaque so you look like you've been painted.