Who are all these people in the Admiral's Club? [closed]

I usually have tight enough connections that I don't have time to go to the Admiral's Club. It's a once or twice a year thing for me, not often enough to justify the $550 cost. Yet, every time I go in the place always has a lot of occupants. Are these (1) mostly people who just fly so much that it is worth the money for the membership? Or, (2) are there special deals and tricks that people use to get membership for a lot less (kind of like the "priority" security line)? Or, (3) is Admiral Club membership expensable at a lot of companies, so it is not costing them anything at all? (it is certainly not expensable where I work)