An enforced mandatory 14-day quarantine could be a serious blow to (not just dive) tourism to (not just) Cozumel. A very common pattern in U.S.A.-based vacation planning is the 7-day trip, often Saturday-to-Saturday. Think about why that is.
Often the traveler, or at least one in a group, has a job. Getting vacation time approved to be off a week can seem like pulling teeth to begin with, even if you've got plenty of vacation time on the books. And in the U.S. we don't get a guaranteed minimum of vacation time.
While the pandemic has brought a lot of attention to white collar jobs where people can work remotely from home, I suspect that's still a minority of the American workforce.
If it's hard to get approval for a week off, now imagine putting in for a 3 week stretch.
Many people have already delayed travel plans for a lengthy time. Last year I didn't do a 2nd dive trip, and my family skipped planning a cruise till this summer (and that's fairly likely to get cancelled by the cruise line). 2021 Is starting to look a to like 2020, with no clear time frame when will all end.
No, I don't see strongly enforced federal quarantines as a widespread routine thing as likely. U.S. culture is more individualistic than that, and the practical demands of life not a good match.