How come people don't say "thank you" anymore?

I often hold a door open when I am entering or exiting an establishment for the next person. Very rarely does the person thank me as if though they expect and deserve my consideration. It frustrates me that society has become this rude and makes me want to stop being so courteous. I’ve found myself lately saying “You’re Welcome!” to the impolite individuals, which totally contradicts the whole principle of the thought.