If app stores allowed paid version upgrades this trend might not have happened.This is a takeaway that I think is really important that a lot of people miss. The problem with the "new" model is that it's created a double-whammy of much lower prices in absolute dollars than we were paying ~15 years ago for software and an expectation that once you've paid that low price, you should get upgrades for free forever. The plateau you mention is, of course, why that can't actually work: most apps don't grow their userbase at a steady rate, they get bursts of new users when new versions come out -- and usually fewer and fewer new users for each new version. If every customer represents one and only one point of revenue -- and that point is a third or a fourth what you'd have charged for the same amount of engineering work under the old model -- this is a death spiral.
Under the "old" model, PocketCasts could easily have been a $20–25 program with $12–15 upgrades when new versions came out every couple of years and it wouldn't have seemed unfairly priced at all. Under our glorious new model, the only way to match this is with subscriptions. And people hate subscriptions. Nobody works out the math to see whether the subscription model actually costs them less than the old upgrade model, they just have a visceral reaction to it.
I get the frustration with any company that charges that low one-time fee, implicitly (or even explicitly, as PocketCasts apparently did!) promises free lifetime upgrades, then goes back on that promise some years later when it proves unsustainable. At the same time, is going out of business or shutting down that product really preferable?