Scratch that, writing any interactive fiction is hard. But writing tabletop roleplaying scenarios is excruciatingly hard.
I have little actual writing experience (mostly from co-authoring the script to a 100-person crew & cast sci-fi student musical) but at least in stage plays most of the writing is about figuring out the characters and making them do interesting things that make sense for those characters.
Now, what is a roleplaying scenario? In roleplaying games, especially when they're played in conventions, a game master writes and hosts a 2-4 hour session in which players participate with limited prior knowledge about what they're about to do. Think of the players as going to the theater except that you're going to be on the cast and make up your own lines.
Think about that. What would it take for you to do something like that?
I think you the player need to feel like you're going to be taken care of, and provided with material that you can make sense of. Roleplaying games make the whole improvisation theater thing a bit more approachable by not having an audience (besides the other players) and not having to move around on stage (unless its a specific type of scenario in which you're supposed to use bodily interaction). But in the end, the game has to be prepared specifically to allow players to make sense of it on the fly.
Modern video games do this all the time: think about the opening of Portal - or even Super Mario Bros. You have no instructions on what the game is about, what you're supposed to do and how to do it. But in a video game the player(s) can only do things that the game was specifically created to allow. In roleplaying games it's different in multiple ways.
First, tabletop roleplaying is an analog game like board games: no computer will suggest or validate actions. The only things you have to guide players are their expectations based on previous games, the responses of the game master, and whatever explicit game mechanics they can read at the beginning of the session - no long rule books!
Second, where board games most often rely on setting up a system up front with all the rules, pieces and goals are explained to everyone, roleplaying is supposed to be mostly imaginary and free. So free, in fact, that if a player comes up with something they want to do and a game master will deny it without giving enough explanation why, the whole group of players can and will call bullshit on the whole game. Roleplaying is terrifyingly free - both for the player and the writer.
And that's what I find terrifying about writing roleplaying scenarios. The trust that people I haven't even met yet are placing on me to take care of them.
I can't let them down.
PS. If you're interested in what I'm talking about, feel free to check out The Laundry World, the Apocalypse World hack that I'll be running the game with, and the full scenario I wrote and ran in Ropecon 2014!