Why Is It So Difficult To Get Rid Of A Teacher??

As I reflect on the number of teachers that are in need of assistance in my building I cannot help but ask why it's so difficult to get rid of an ineffective teacher.  After observing their class and finding areas of concern principals have to collaborate with the teacher to create a plan to help the teacher 'grow'.  Inevitably this plan becomes more work for the principal than the teacher.  Between the documentation and the follow up meetings little time is left for the "good" teachers.  Just like with students, most of our time is spent with the teachers who are making the wrong choices and wrong decisions as they try to educate our students. Now I'm not saying that teachers don't need guidance and shouldn't be allowed to grow and become better; but at what cost.  How much time should ineffective teachers have to damage students?  Students will never get that time back.