There are many free programs because people believe that:
1. The product should be available by use for everyone, or is a tool that should be free.
2. No one would pay money for it.
3. Other products are free and do the same thing, so their product won't sell if they charge.

While other programs, such as Photoshop, are much better than free programs available, and people want it so they can sell it for as much money as they do. For example, MS Paint is free and comes with any version of Windows since maybe as far back as Windows 3.1. I'm not sure. Compare it with Photoshop. Both are theoretically the same in concept, that you can make pictures with them. But Photoshop is so much more extensive, easier to use, and has so many more features, so they can charge money for it. If you didn't have MS Paint on your computer, and you couldn't get it for free, would you pay money for it? I know I wouldn't.