Why are so many Amnesia custom stories so similar?

[cav500]

I am new to playing Amnesia custom stories but so far I have downloaded and played through around 100 of them. This has taken me several months to do. One thing I have noticed is how similar many of them are. Lots of them have this same formula:

1. Starts off in the same typical bedroom with a door that is usually locked for some strange reason.
2. Then you move to the hallways of the same typical house on a search for keys and tinderboxes. Tinderboxes are always a sign that the story is going down to the cellar, as usual.
3. Then it moves down to a typical underground/cellar/basement/prison area where you spend most of your time with the monsters.

Why do so many of these custom stories follow the same pattern?

I also play a pc game called Thief where fans of the game have created some AMAZING fan missions using the engine that created the original Thief game. These missions are all so extremely different. But with Amnesia, it doesn't seem that way unless it's a full mod with it's own bat or exe. file.

Just wondering. I've never tried to create a custom story so I don't know how limited the software is for creating custom stories. Has anyone else here wondered why these custom stories are so similar?