It's a strange concept, but just because someone has a minhag not to eat someone else's food on Pesach, doesn't mean they can't make money selling their food to people without that minhag.
I'll grant that the "mishing" minhag, and various other family minhagim (don't eat unpeelable vegetables, don't eat chicken, etc) throw a monkey wrench into my theory.
I don't know these ppl personally.
I'm sure some programs are run by non-mishers who think that their own program is mishing (and I won't question how they apply their minhag, although I'd have thought it's more akin to your own kitchen where you hired people to cook for you, which I assume mishers are ok with.) And I'm sure some are run by people who don't eat tomatoes, but don't want to have a program with no tomatoes.
But it seems like the pesach hotel world is full of people running programs, and attending and allowing the program to advertise based on them, and then they don't eat from it because they don't want to eat from a program at all.
Suppose you found out that all the ppl you'd seen eating at the Waldorf Jerusalem were actually being given free stays to pretend they trusted the kashrus, and were eating homebrought food.