Too small a market to justify a marketing expense, too painful to write for you own commercial self-interest to give it away.
Before there was free software, there were a LOT of share-ware apps that people who make a little bit of money with. A few people got rich, but most people got enough to go out to dinner occasionally.
GPL apps show up, do 95% of everything share-ware did for free, which means the remaining 5% got lost in all the noise.