For OsmAnd at least, that seems to be per-county decision, as capability seems to be there.

E.g. Argentina standard maps are more than 700MB in size for whole country, but you can choose to download e.g. just the Mendoza, and that is more acceptable 26MB.

OsmAnd also offers smaller road-only maps (379MB for whole Argentina, or 15MB for Mendoza) if that is enough for you.

So if your country does not offer such subdivisions, it might be simply because no one requested it yet. So you may want to head over to https://github.com/osmandapp/osmand/issues and request it.

Also, OsmAnd allows you to export and import maps, so perhaps local communities could organize to download the maps once from the Internet and then share them locally among themselves.