Because modern credit card networks and payments gateways have virtually zero friction now so subscriptions are a no-brainer for everything.

It takes the same amount of effort to setup a recurring subscription stack vs a one off payment.

That lack of friction also allows that subscription to do a recurring charge every month out of sight and even auto renew with an email that will be lost in the noise.

I might pay $5 to find out if your app is even useful. I will not pay $5 recurring monthly for an app I forgot existed until I notice it on a monthly credit card bill sometime in the future.

What I want is a one month subscription. I’ll sign up for recurring if I want to but it would require explicit action.

But nobody wants to offer that so they don’t get me at all. I assume there are others like me, perhaps even dozens of us.

That doesn't answer the question that was asked. The person above didn't ask about the workflow of negotiating recurring vs. singular payments with financial services. Some other 'mysterious' factor pushed this business to monetize their non-recurring service with a recurring payment. The question is if there is even a semblance of reasoning to make this a subscription (especially one with this kind of a pricetag), or if they made a purely local app once and just wanted to rent it out for more money.