Most of people give the reason that in American culture believe that everyone is equal so, the value of seniority is so little but in Thai culture need you to act politely to elder people.
You can not say any bad words or act rudely to them. For example, you can not say sa-wad-dee means hello to elder people because it used for friend but you have to say sa-wad-dee-ka to makr it sounds more politely.