There is a huge difference between code and my stuff in my house: code cannot be stolen, just copied, therefore your analogy fails.
Imagine this: someone comes to your home, likes your decoration and decorates his home in the same way as yours. What are you going to do now? Sue him? Put locks on the door and never let anyone in again? Force people to wear blindfolds inside your home? Or just accept that no one harmed you in any way by using the same interior decoration?
As I said, most people don't get it. However as a fellow mod author, I do. People treat anything on the computer very lightly, such as stealing. Most people don't care about getting a copy of a cd from a friend, a movie from the internet, or even pirated software. This is illegal activity, no ifs, ands, or buts. This is the same thing. Many mod authors don't like others profiting off of their mods, their hard work for code. Which by the way, can be stolen, by definition, because it is copyrighted material, and protected by user agreements. Therefore your analogy is completely irrelevant. What you are referring to, is an idea. The idea can be copied, such as your analogy, but cannot be stolen. However code is physical, not psychological, and can be stolen. In conclusion, these mod authors work very hard to make a mod that they want to play, and graciously share with the community.