I still have my CD for Office 97 and (somewhere) SuSE Linux 7.2, but I can't honestly say I can continue to use those.

The way to get around that is either continually releasing feature upgrades with one-time payments, or paying for access to the software only while you need that access.

Both models have strengths, one is not inherently evil and the other inherently good.

It's easy to say app updates should be bundled into the one-time cost but even that needs to have a time bound on it. When software lasted 3 years that potentially made sense, but now the release velocity is so much higher that there would be an explosion in complexity to try to keep up with all "one-time" releases going back for years.

Even completely Free software packages struggle with the balance with how far back to claim prior releases are under maintenance (e.g. LTS is popular, but so are 'rolling releases'). That's because of the underlying economic complexity with the costs to maintain what has gone before vs. the cost to develop what will come next.