There's no reasonable devil's advocate. The answer is that one-time fee apps are not sustainable. There are ongoing costs with most businesses and one-time fees do not capture that. Therefore don't sell them. Sell everything on subscription or you will eventually fail to serve your customers and everyone will be unhappy. If you're a big business, it's risky to buy open-source applications, so don't do that unless the benefit is obvious.

They promised a thing they could not deliver on and that was sufficient to get enough users that they could then sell the app onwards to a bunch of suckers. This is a classic play in the "sell dollars for pennies and then sell the dollars-for-pennies app to a guy with a lot of dollars who eventually gets sick of buying pennies with dollars" genre.

The one time fee doesn't pay for your ongoing costs, but it does pay for your upfront costs. The trick is to either get other users to pay for your ongoing costs, or to reduce ongoing costs and stop further development.

One time cost per major version is sustainable, you won't get Silicon Valley rich on it, but you can make a living.

Lifetime licenses only work in the beginning when you have people buying them at regular intervals, at some point the market is saturated and you need to have a subscription model.

Case in point: Unraid. I have two grandfathered "forever" licenses and I'll never need a third.