This is where I get to with a lot of non-crazy people (the crazy ones just won't pay for software). Since you are fine paying $20 for a useful app, a $7 a year subscription can be better than a $20 one-time purchase in meaningful ways.

It aligns your incentives with the developer very well. They really want you to not cancel your subscription after only paying the first year's payment (when you may not have even paid back the customer acquisition cost!), and you want the app to be high quality and well-maintained. If the developer doesn't meet your bar for that, you cancel the subscription with 4 taps and they lose future income. That incentive to please customers after the sale just doesn't exist in a pay-once app world (except in tiny niches of old-school developers, like the Panics of the world, whom I do greatly respect).

Besides the incentives, it also gives you a chance to, after that one-year $7 spend, re-evaluate "do I even use this anymore?" If you paid for a guitar tuning app and you stopped playing guitar, you can just cancel the subscription, even before you've paid the amount that they'd have priced it for one-time-purchase. There is upside for the consumer in the apps that either let you down, or that you simply realized you no longer need, and it lowers the risk bar to try an app that you aren't sure about.

I get that if you do end up using such an app for the next 15 years, yes you'll probably pay somewhat more than any price you'd have considered paying one-off, but it also probably means that app (an app you use often for decades) couldn't have been sustained for all that time with only new customer installs paying the bills.

> if you buy a book, you can read or refer to it every day without paying again, or you cna listen to your favorite songs as often as you like by playing the CD.

We agree that this is all very great. And since the music or book you buy carries zero support burden of any kind from the artist it's a pretty great model - after their album launches the artist can devote 100% of their bandwidth to producing new music, or they can tour to get recurring income out of the same music, or a mix of the two.