You're supposing total information. You're supposing that no one can be screwed unaware.
Actually, most people don't know a thing about the issues around proprietary and free software. If they did, I am confident that most (more than 50%) would rather buy free software.
Now of course those who sell proprietary software happily buy proprietary software: they often don't have a choice. They can't use GPL software. They can however, use BSD licensed software. And I bet they prefer that over proprietary products.