They have to read them. It's not a census if they don't. And they pester people because their supervisors make them. And their supervisors' supervisors make the supervisors be strict with the census workers. And the supervisors of the supervisors of the supervisors, etc, etc, etc... all the way up to the people who run the whole show, who are accountable to the US Constitution, which is the highest authority in the country, and a damn fine one, too if you ask me.

There are good reasons for the questions they ask and the methods they use. The census benefits the voters. Answering the census is as much a civic duty as voting.