A friend recently suggested that I ought to be teaching teachers how to write and produce musical plays with children. I was flattered by her suggestion, and yes, I do believe that the way I did musicals with children was somewhat unique, and worth teaching teachers. But I also realized, as she was talking, that sharing expertise involves complicated feelings. And as I think about other teachers I know, I don’t think I’m the only one who finds the subject complicated.
Some teachers don’t really believe in their own skill. They think they’re fooling people into thinking that they’re doing great things, and they don’t want to be found out. They imagine starting out some workshop by telling what they do, and immediately being interrupted by another teacher who does it MUCH better. Rather than risking that, they keep their “gifts” to themselves.
Even teachers who do believe in their own talents still may be reticent to go public. Teachers try to see each other as equal comrades, and as soon as one teacher allows himself or herself to be singled out, that comradeship may be in jeopardy: “Who does she/he think SHE/HE is?” Schools are supposed to be communities of learning, but feelings of competition can get in the way of such community – can pit people against each other.
Another possibility is that a teacher who does something well may not think he or she can teach others how to do it well. I’m reminded of a limerick I once heard:

A tutor who tooted a flute
Tried to tutor two tutors to toot.
Said the two to the tutor, “Is it harder to toot,
Or to tutor two tutors to toot?”

Sometimes it can be much harder to tutor the tutors; some people find teaching some skills too hard. Sometimes those who can’t teach, do.