What is it about DMing that makes it seem like such an impossible task to most people?

I'm going to add in my own two cents, though it'll probably get lost. I don't have time to read the thread (I have a campaign to prepare!), but here it goes.

DMing is performance art. As a DM, you're a performance artist the same as a juggler or a magician or a stand-up comedian or an actor. A DM can (hopefully) sit at a table and weave a story from some notes and keep 4-5 people enthralled in the story for 3-5 hours.

A juggler can go home and spend hours practicing juggling. A card magician can practice his elmsley counts and center tears in a mirror until they are absolutely perfect. As a DM, I can prepare, but my practice is all at the table. It's a bit like stage hypnosis in that way--you can prepare but you can't practice without someone under.

And that's really scary. Because practice is where you find out you're bad at something and improve it. And you're doing it in front of other people that see how bad you are at it. It requires a special sort of person willing to do that, and not everyone is up for the challenge.