The only answer I can think of is that your divemaster was mad at you and didn't actually take you to the reef!
How many days did you actually dive? And if you care to share, WHO did you dive with that showed you the worst of Cozumel diving?
Maybe they heard all the "WestPac" talk at check-in and just gave up before they even had her on the boat.
I have a friend who's dived just about all the top spots in the world, many by liveaboard since that's the only way to get to many of them, and I just love going to the Caribbean with him. He's always like a kid in a candy store. I don't think the guy has ever come up from a dive where he isn't beaming about something he saw, encouraging and genuinely excited about another divers first, etc. He is just a pleasure to dive with...even when we've been in some places where there really is just clumps of coral and sand.