For one thing, I simply cannot imagine on a daily basis walking into a room full of dozens of adolescents with noise makers in their hands. Granted, my background includes dealing with emotionally disturbed adolescents both as an attendant/group leader and as a music therapist, and one assumes "normal" adolescents don't present as many behavior problems. But still, my hat is off to anyone undertaking such a daunting task.
Music educators also have to be familiar with all the instruments and how to play them and their myriad idiosyncrasies, along with being able to transpose all kinds of stuff in their head and in general having what I call "theory mind". It's all way beyond me. I was amazed to discover that horn players are expected to be able to transpose in all sorts of ways when sight reading. If I were to devote myself to that and no other musical tasks I might become barely proficient, but it's not playing to my strengths, to say the least.
Music educators also have to be concerned with preparing their best students to be ready for the next level of achievement. If this were not the case, the feeder system would break down and we wouldn't have good numbers of people ready to play at the high level needed for professional organizations.
On a more general level, educators are tasked with preserving the canon and the playing styles needed to present it as it's meant to be played. Without that, entropy would set in and all kinds of beauty and technique would be lost. There's more to making music than the printed page and music educators have the mission of preserving that which is beyond notation, yet so very crucial to successful presentation of the canon (whether Beethoven or Sousa).