I echo everything #7 said; I also teach both levels and have had the exact same experience. College professors are not paid to be interesting, they are paid (in part) to transmit information to those willing to learn. Additionally, most college professors have not been trained in teaching methodology. They know a tremendous amount about their subject, but they have to figure out on their own the most efficient way to pass on their knowledge. K-12 teachers are trained to be teachers; they know less about the subject matter, but much more about the way others learn and how to create lessons in a variety of different ways.
A K-12 teacher spends a lot of time planning how to teach material and creating tools like powerpoints, games, worksheets and activities; that is part of the job. By contrast, college professors are expected to spend their non-class time doing research and writing for publication. The job descriptions of the two groups are totally different.
Additionally, in public school the teachers are trying to reach every student, including those who don't want to be there. In college, students have chosen to be there and are expected to act like it.
In public school, education is the teacher's job. In college, education is the student's job.