As a software developer, I experienced the need for subscription revenue first hand. Regular users want support for their software and there's only so much you can do for a fixed one-time payment. As an example, Windows might update on their computer without their knowledge but that Windows update breaks something so the user is like "I didn't change anything but your app stopped working" and in that situation you're supposed to sell them a paid upgrade to the next version?

As a user, I share your concern. To me, SaaS means I might end up with files that I can't open anymore because the app needed to open them was forcibly upgraded.

In my opinion, the solution is what JetBrains does. Regular subscription payments but you get perpetual licenses so you can keep using old versions as long as you want.