i’m guessing what you’re asking for in terms of providing offline map data + mappable observations in an app would be super complex from a technical perspective. i suspect the benefit likely would not justify the cost to do this.
i’m not sure which app you’re talking about, but in the Android app, there maps available in the Explore screen (as long as you have a data connection):
you may want to read this other thread, too: https://forum.inaturalist.org/t/locally-store-map-tiles/3457. it’s sort of in limbo and it doesn’t directly discuss what you’re talking about, but it might give you a sense of what others have said about offline mapping in general. for example: