Why are the comments of politicians directed at education so often negative?

When educators talk about education they tend to say it is important but then are critical of educational practice. Standards are too low. Teachers are lazy of incompetent. Costs are too high. Teachers hide behind unions. If you work in the field, the negative attention gets tiresome. It also seems that turn-about is not allowed. Educators are discouraged from being political unless their efforts are disconnected from their classrooms. 

There is good news and there is bad news. This article from Forbes claims that the politicians are going to back off criticizing k-12 and will focus more attention on higher education.