Why. Are so many people diving air in Cozumel? Is nitrox hard to get? It's been 15 years since my last Coz trip so I wouldn't know.
In Bonaire and Hawaii, we often do 5 dives a day (shore, includes night dive). I have a hard time imagining 3 dives running up to NDLs, unless one is using air. And, why would you limit yourself by using air while on a dive trip to a place like Cozumel?
Unless you're just really into the party scene, I don't see that Cozumel has a whole lot of other things to do besides dive. Maybe go to the Mayan ruins one day or a whale shark trip.
1. they are cheap, or;
2. They are hoovers and it doesn't matter, or;
3. they get a little deep for nitrox.
My guess. I always dive nitrox.