Why are the majority of government workers so rude and impolite?

Every time I have to visit the US Post Office or DMV, the clerks in San Diego, CA 92103, are extremely unpleasant without any discernible cause. Especially with people who speak with an accent. They appear to be acting impolitely, rudely, or inappropriately just because they can. Most individuals are accustomed to keeping their lips shut and moving on because if they say anything, they risk getting into trouble. Could you please comment on this matter?

Thank you.