Absolutely.  It easily takes 3 hours to prep a 3 hour class.  And to mark a decent sized assignment for 30 to 40 students often takes 15 minutes per assignment.  Even if that's not every week it's every few weeks.  Faculty easily spend at least twice the amount of hours working outside class than they do inside.  We also have regular office hours, help students by email, do research to keep current in our fields, manage curriculum, and more.  There's tons of work to be done outside the classroom.  You probably have never tried teaching a college course.