People are so funny about software pricing. There’s somebody on the other end who has to make a living to maintain and improve the software. And doing one-time pricing means you have to pursue user growth instead of sustainability. You also might be forced to charge for major version upgrades, fragmenting the user base and adding lots of complexity and overhead. What’s the maintenance expectation on a one-time purchase from a small company? Keep it working forever?
As a software developer myself, like many of us here, I can assure you that I'm very familiar with the concerns mentioned; in fact, I've already provided examples in this thread of companies which directly consider them into their pricing model in order to provide versioned licenses.
It's kind of surprising to have to say this though... 10 years ago and beyond this was the norm, if not the only way. Software companies figured it out a long time ago. A one-man company or a side project is a different thing with more constraints, but that's not what this is anymore.
There's also the philosophical angle of creating software that cannot be bought or owned. That strikes a nerve with a lot of people (especially on HN).