We used to dive in February every year for a decade due to "February school vacation" and again for "Spring vacation" in April. We're always on the island in May because that was our daughter's birthday. Therefore I feel qualified to comment.
Streydog is right. Come sooner. northernone and uncfnp provide the right reasons.
If you can't stand the idea of a possible port closure due to weather, which is not something that affected us much in many Februaries, wait until Spring. I LOVE February in Cozumel. Sure, part of that's because I'm not in NH in February, but it's nice weather and the spotted eagle rays are more plentiful. It's high season, so some things such as accommodations are more expensive. We actually avoid Carnaval activities as much as possible, so for us that's a minus, but many people love being on the island at Carnaval.
Early April is glorious and hardly ever hot and muggy. By May, it's often hotter and more humid. Some places count late April as low season, though for most it's still High Season until May.
It seems plausible that your trip options are timed based on school vacation times. If so, airlines know all about that and will jack up airfares from your area (they're roughly double during New England's February School Vacation week what they are the week before or after). If not, then it's possible that travel costs might help you make the decision.