I agree... though just because one can do something doesn't mean you can do it well.
Sure, but the only way they'd ever be able to do it well is if people are willing to let them do it. And of course, they have to be willing to try.
So it may be...
scarier than being a player
more (something) to handle than being a player
more time than being a player
more/different skills than being a player
Sure, it is all of those things. But is it SO much more those things? And if so, must it be so?
For example, there have been comments in this thread about needing to build a game world for 12 to 18 months before involving the players. That's a lot of time, and while it may be perfectly enjoyable to the person doing it, and it may be exactly what they want, it is by no means necessary.
I don't think that GMing must be significantly scarier, more involved, or more time-consuming than playing.
I disagree here... if more people want to GM they should... but honestly that doesn't seem to be the case. There has to be a reason for that.
Well, I didn't say more people wanted to. My point was that more people can do it than currently do. I think some are turned off by it, for sure, but I think a lot of that boils down to perception. Not always of course, but I think very often players have been conditioned to believe that D&D or RPGs in general are significantly more difficult to run than to play....mostly because of the things you listed above.
I don't think that's actually the case nearly as much as it is perceived to be the case.
I also don't think this is an area where D&D does itself any favors in the way it's structured.
I agree here as well... I enjoy it but I have been on both sides of the screen and my experience is that being a DM is all the things you said above... It's scarier (especially the first time) than being a player because unlike a player I don't have a group of other DM's at the table I can draw from, acquiesce to if I need a moment or follow the lead of if I don't want to be front and center. There's more of everything to handle than being a player, from descriptions of people, places and things to roleplaying NPC's to keeping the lionshare of the mechanics straight in order to make rulings to improv'ing... there is more. It takes more time than being a player, because as a player I can, if I choose,literally not think about the game until the second we begin play and I'll do fine, maybe there are DM's out there like that but I've needed to do at least some minimal prep work before a game session to feel comfortable enough to run. Finally the skills are different... screen time management, pacing, acting, the ability to clearly describe various and numerous things, and so on. These are skills a player doesn't necessarily have to bring to the table but are near necessities for running a good game.
EDIT: Also many DM's tend to be the host, set the schedule, get the group together and so on. I guess what I'm saying is maybe it isn't hard to be an above average DM but maybe, just maybe it's more effort than most people are willing to put into a leisure activity when they can just play.
I think players tend to have those skills, too. They're typically not required to use them as much as the DM in a game of D&D, but that doesn't mean they don't have them. Or that they can't get better at them.
But to comment on some specifics you mentioned.....I do think the DM has other people at the table he can lean on when needed. There's no reason that he can't ask the players questions to get inspiration, or to have them help with descriptions or other things. I absolutely involve my players as much as possible. Not just to engage them even if it's not their character's turn to act, but to give myself some new input on which to build, or to buy myself a moment to come up with an idea, or similar.
D&D does require prep of some sort, so yes, it takes more time to DM than to play. Are there was to mitigate that? Absolutely. Some folks may claim otherwise, or others may enjoy the effort and not want to cut down on prep time. But it can be done.
These things can act as barriers to people trying. Tell someone they need to build a world for over a year before they can begin play? That's gonna be a small list of people who think that makes sense.