I find it amazing that this question is being asked. Perhaps it is because the question is posed wrongly. It should be, Why do people freely share their creations? Because people create. We love to create. The desire to create can outweighed any compensation you may get for that creation. You want to give your creation life by sharing it with others. And if they take your creation and build on it, then the birth has been successful and your baby will have a life of its own.

People don't ask why painters paint pictures that will never be sold or write books that will never be published. But cross the line to technology and they fail to see the same creative energy at work. We understand the proliferation of blogs and websites as something arty. Why not the plethora of freeware and open source programs? Why are such creations explained away in terms of personal gain? "... writing open-source software increases the authors' prestige among their peers or gains them experience that might help them in the job market..."

Creating software is a precise form of art that may capture the creator's imagination as much as any poem or drawing. If you are paid to do what you love then that's great. But either way, if you are an artist, whether analog or digital, create you must.