> strongly doubt that this company runs their own weather stations or meteorological models. Their only recurring cost is API access to the companies that provide weather data

No. But I'd suspect a tabula rasa approach to weather–particularly given it hasn't been rolled out globally in one go–incorporates satellite data, local measurements, et cetera.

Again, that may not take constant subscriprtion. But it does take constant expert monitoring and awareness.

> Considering that there are many free weather APIs

If you're a glorified viewport into these APIs' data, you may be able to stick with their most-static data and fire and forget. In reality, what those outputs mean change as the models and techniques evolve. There are new APIs with new data constantly coming out, and they're often adding connectors.

> a weather app shouldn't have large maintenance costs that couldn't be covered by a one-time payment

The only way I see this working is if the user is explicitly aware the app can break at any time if one of the APIs change anything, which they often do, and that this may not cause any obvious failures, just a decay in the app's accuracy or usefulness.