Teaching skills for a PhD holder

A PhD holder knows something that is unknown to whole world. If the PhD holder can’t explain and communicate that knowledge properly to next generation (written or verbally) then, most probably the knowledge might die and disappear with time.

Writing and speaking both are art.

Extrapolating same analogy to the teaching, who should teach a class, a topic expert with additional information + experience than books (PhD) or a text book orator. Text book orators are good teacher initially, but PhD holders are expected much more for positive reasons.