Why Do People in Sales Torture People?

Why do people in the sales industry tease and torture consumers? Whether they are selling airline tickets or blush blazers, they put out a product "for sale" to get you interested, only to take it away! How can an airline sell you a ticket, give you a reservation, then change your flight to a different day because "oops, we oversold"?  Then when you become irritated because you have to cancel your trip, they act all shocked and appalled like, "What? You're angry?" Don't they realize that the reason people make reservations for specific days is because they have to be there on that day? The important part of taking the reservation is keeping the reservation. "Oh, just tell the hostess of the party you are attending to change the day of the party because we screwed up and overbooked". Idiots!!  And what's with the scarcity of blush blazers in size 2?  A large franchised store comes out with a new line of blush blazers and within a week all size 2s are sold out across the country? And you're not making any more? You've got to be kidding!