When I first dove Cozumel near the end of the last millenium, the DMs I used never deployed a DSMB. I had never even seen one myself. A few years later, deploying a DSMB before surfacing seemed to be the norm, at least with the DMs I had. That's when I bought my first one.
I am guessing it has been at least 10 years since I first recommended on the Cozumel forum on ScubaBoard that SMBs be required in Cozumel, if not by the local government then by the dive operations. I wrote that in a number of threads. I got pushback from people saying that requiring SMBs would be so costly it would bankrupt some dive operations. Seriously. A dive operation should be able to get them for $20 or so. If you tell people that if they don't have one of their own, they can rent or buy one from you, I would guess they would actually run a small profit on such a requirement.