I can think of at least three people in my circles who share at least one of your three reasons for finding GMing difficult, and I can think of at least one other who routinely has routinely needed breaks from it to reassemble in his head how he wanted to do it (though the last friend has mostly lost the hobby, I think). Obviously, some people won't find it easy, and some people will enjoy it less than others. Human variation is real.Hello. I'm one of the supposedly rare specimens that find GM-ing very difficult.
In addition, I also had a really bad experience (as a player) once with another player, which lead to me severing my relationship with them. This experience haunts me to this day, and makes me extra anxious about running or playing games with new people.
- I find improv hard. It's very difficult for me to handle situations that are far out of what I've prepared, and that happens like all the time.
- I find people management difficult. Dealing with people who are late or disruptive. Or how to give them the plot hooks they are interested in.
- I have a hard time being in the spotlight. It gives me a lot of anxiety, and it doesn't feel like it gets any easier the more I do it.
To sum up, I absolutely agree that DM-ing can come more naturally to some folks—my partner, for instance, who spends less than a fraction of time reading / researching, runs absolutely banger sessions. But I am not gifted with the social & improv chops. And I didn't start the hobby at 10 years old with lots of room to fail and retry.
EDIT: Changed generalizing statement in final paragraph to make it specifically about me. "Not everyone is gifted" => "I am not gifted" & "Not everyone started the hobby" => "I didn't start the hobby"
I hope you at least get some enjoyment out of it.