Whether it makes sense or not, subscriptions feel more expensive than one-time payments. You could pay for an app and only occasionally use it over the course of several years. You could ignore paid updates released on the meantime, and still enjoy the app that you bought back in 2015, at no additional charge.
The most prominent example of this category of apps, off the top of my head, is Acorn. I don’t need the app on a regular basis, but when I do I’m happy to have a powerful tool at the ready.
Sure, it would be possible to sign up for short-period subscriptions, but that sounds like at least a mild pain in the hind quarters.
Last year, paying for a subscription of Bear was a no-brainer. The app is such a joy to work with. Despite the obvious overlap in functionality I would have no problem using Ulysses and Bear side by side going forward. But this will have to change.
The thing is: I can use Ulysses for what I use Bear for2, but I simply can’t use Bear to replace Ulysses functionally, not even close. And if I have to chose between the two to keep the costs low it is obvious that I’ll be terminating my subscription to Bear.