Most weather data isn't generally available by easy to query REST API's (at least not at the original sources). One side project I had I wanted to use NOMADs data, and it was quite a grind downloading and processing the raw datasets into something usable at an application level (or viable to expose via an API).
That’s why you have service/products that have the sole purpose of taking all these region specific data sources and processing them in to a generic json api.
The government orgs probably do it intentionally so they don’t have ten million devices pinging their servers to update weather widgets.
