Not that it's okay, but App Store/Play Store do the same. They don't refund for apps that have become unavailable.
It's nothing special, just a location tracker that logs to a file every so often based on time and/or distance moved (could also ping a URL with encoded location info instead). Basically the underlying data for location history without relying on Google. Its notable feature years ago was that it would do location 'steals' - instead of just triggering a then-expensive location check, it would grab the most current available location info as triggered by some other application and only force an update if that information was too old.
Don't make excuses for Amazon, please.
What are some well-known apps sold as one-time purchases now?
What I've heard is that one-time purchases lead to a lack of income after three years, when people expect upgrades. That's not a problem for app developers who don't plan to do any upgrades, of course.
Notably I'll throw in a few things like PocketCasts, Nova Launcher, Gentle Alarm by Mobitobi, a variety of camera and gallery apps. Some of those shifted to subscriptions (PocketCasts after being sold twice), others just got shuttered.
i'm not in the habit of buying apps anymore. I did drop a lot of money on the wolfram alpha iOS app when it first launched (it was over $50 at the time iirc, but to hedge i'll say "adjusted for inflation")