Green Bay is a city of 100,000 people that has its own NFL team.

So yes, every Green Bay Packers game is a sufficiently big event that the Hyatt Diamond Availability Guarantee doesn't apply.

Or, more generally, any event is a sufficiently big event that Hyatt can determine that the Hyatt Diamond Availability Guarantee doesn't apply. Thus, the "guarantee" is just marketing speak, and isn't a real guarantee at all.