Most people are programmed to say certain things

There's no need for a full thought process. If anyone says "Thank you" to me, my response is always the same "You're welcome", then " Have a great day" . Some people like to say : 'You are most welcome' or 'You're more than welcome'. And they don't need to find other ways to response to " Thank you" anymore. I mean, if you work on customer services, you probably have to say the same thing hundres of times a day, then you're done being programmed. 

Our brain is wired to find the easiest, less energy consuming way to operate.