Not sure if you're a dev yourself, but I don't think yours is an uncommon feeling among developers reacting to pricing.
[TL;DR - I think our expectations are out of whack though]
Why do you think this is, though? As a developer, we know that all code has a carrying cost, and that when building on the sand that is the iOS SDK, that almost mandates at minimum a yearly compatibility update, and possibly occasional significant rewrites if some critical SDK feature is removed or broken. Also, this app is building against a third-party (HN) api as this one does, which could change at any time and require the developer to update the app to be compatible. Having a periodic subscription is the only way to align developer and user interests -- they need to keep earning your money a little at a time, and as long as there is a good audience, there is a matching revenue stream to justify continued maintenance on the app. A one-time unlock front-loads 100% of revenue, making all maintenance work have negative ROI unless the app experiences constant, consistent growth forever. And there's certainly a limit on how many people will ever regularly read HN. Eventually that ceiling will be hit, and the app's revenue could drop to effectively zero, even if a million users count on it daily.
As humans though, especially analytical ones who are keenly aware that $1 a month for the next 10 years is $120, we hate to think of spending an 'absurd amount' like that on any apps unless they fit a certain mental model (it seems things like Spotify fit a profile that we understand comes with monthly bills attached). But I think it's odd that, while we would feel completely fine spending $6 about once a month for an ice cream cone, Starbucks, a package of cookies, etc. we balk at the prospect of paying even $1 a month for an app, even when it's an app we use daily, like a podcast client or, for some, a HN app.
I think I place the blame on the expectations accidentally set up in the 1990s, when software for most consumers was preinstalled (thus invisible in cost) and everything else was "one-time" because both the need and the ability to distribute updates regularly was so much less. I assume companies like Microsoft and Adobe who did need to maintain their software could count on the massive ongoing computer adoption in that era to make them profitable even when many end-users would decline paid updates once the apps reached a certain level of maturity -- which I think was the predominant practice among anyone except certain classes of "professional" users. While I agree some apps are out there that charge say, a $19 monthly subscription to crop images, just exploiting ignorance of customers or preying on children, I think we should normalize apps that receive maintenance having a subscription model.