TextExpander is a good example of this. They changed from a $45 license to $40/year subscription. It's a well polished piece of software, and it syncs between Mac and iOS and has an iOS keyboard to facilitate use there. Quality stuff. But when it comes down to it, some people just want simple text snippet replacements on their Mac, and you'd be an idiot to pay a yearly fee for that.
Obviously I don't have TextEpander's customer/sales information, but I assume more than a few users jumped ship to aText's $5 one-time-purchase.