The business reality is often not understood by the users and that's why every company is moving towards SaaS, it allows the company developing the product to continue to stay in business rather than providing a product then shuttering because it couldn't sell enough.
The former is simply more sustainable than the other, much as some (like the vocal minority) might disagree with this fact.
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That being said, there are many who sell one-time licenses, especially in the indie hacker space on Twitter, such as NomadList and BoltAI. Their model works because they make enough money from their products to retire on, as solo devs, and their products aren't necessarily ones that require constant updates (well, maybe BoltAI as new AI advances come out all the time that need to be implemented, such as RAG, parsing PDFs, storing "memories" like OpenAI, etc, but most advances come through new models, which is just an API call away).