What is the most useless app that you have seen being given as a subscription?
For me, I tried a 'minimalist' launcher app for Android that had a 7 day trial or something and they had a yearly subscription based model for it. I was aghast. I would literally expect the app to blow my mind and do everything one can assume to go that way. In a world, where Nova Launcher (Yes, I know it has been acquired by Branch folks but it still is a sturdy one) or Niagara exist plus many alternatives including minimalist ones on F Droid, the dev must be releasing revolutionary stuff to factor in a subscription service.
Second, is a controversial choice, since it's free tier is quite good and people like it so much. But, Pocketcasts. I checked it's yearly price the other day, and boy, in my country, I can subscribe to Google Play Pass, YouTube Premium and Spotify and still have money left before I hit the ceiling what Pocketcasts is asking for paid upgrade.
Also, what are your views on one time purchase vs subscriptions? Personally, I find it much easier to purchase, if it's good enough even if it was piratable, something if it is a one time purchase rather than repetitive.
Downvote instead of answer, nice.
I think people don't understand your question, or think it might be sarcastic. So to answer your question: server storage and computation power costs money. Depending on how your app's backend works, this can be cheap or very, very expensive, paid monthly or yearly. It also needs to scale with the number of your clients actively using the backend. Some of us just sit on the costs to give its users a free and ad-less experience with more functions without taking any money (by the thought "I pay for this server anyways, so why not share it"). But it costs me more, if I have more active users and I have to actively compensate this.
But there are also some greedy bastards, taking much more thinking to get rich with a single app (actually met one of this devs)