As a quick answer, I would say people appreciate what they pay for, and do not care about what they may have for free. Professors are respected, and even teachers at private schools, as are professional tutors. But when teachers are used, it usually mean public school teachers, who are essentially free (taxes notwithstanding). To spread science, keep it secret extends to education and educators as well. If educators were rare, expensive keepers of knowledge, then they would be coveted.

And of course, since the government is the largest employer of teachers, they are able to keep their salaries low, leading to a decrease of prestige and quality of teachers. Which leads to a vicious cycle downwards.