The issue is not the sharing of ideas, but sharing of how the software was made. It is more like saying: "if I buy your food, you have to give me the recipe or I will sue you." There is a huge difference between using gcc and knowing how it was created, for example.

Nobody is restricting you from creating a similar food or software (unless there is a patent, which is an entirely different issue). You have the right to create your version, and I have my right to sell only the product, not the process that made it.