I'd go a bit farther: not all software can be sold. Making some extremely niche software fills that niche, but there may be a very small audience for, say, combinatory logic interpreters, or theorem provers. If we as a society demand that every piece of software be sold, and maybe the bulk of the members of the society have a weird idea that the price of something has to reflect the cost of that good plus profit, then a lot of software will never get written, and a lot of ideas won't get tried out, and a lot of niches will go unfilled.