Doesn't answer the question why nobody has build an interface like the first example over the low-level libcurl bindings, or if someone has done so, why it hasn't been more popular.

I'd guess: because distributing packages with native dependencies is sort of a a pain, and was way worse in the past, especially cross-platform, and thus python-only packages are preferred. Leaves open why libcurl bindings weren't choosen for stdlib.