The airlines have an arival time at the gate requirement for every flight, normally an hour. They sell standby tickets for just such issues as no-shows and people late to the airport, etc.
Not accusing but asking... were you at the gate within the timeframe given on your docs? If not they had the right to offer those seats to another traveler. Insurance helps in cases where you were not negligent. Even if you'd purchased it and did not meet the recommended arrival times, your claim would be denied.
Everyone seems to believe that the cruiseline air package is a safer way to go than booking air on your own. They take no responsibility for the airlines delays/cancellations. Read the docs they send but nobody ever reads. They distance themselves from any liability/responsibility well and have good lawyers to back their position. The airlines do the same. I'm a believer in travel insurance for these and other reasons but the traveler has the ultimate responsibility to plan well for extra time getting to the airport and planning for delays for traffic, long lines, security, etc.
Again rwiebe13, not blaming you. Just wondering as I'm an agent and have similar situations more often than I'd like. Hoping I'm way off base and something else was the problem.