The devs are unwilling to automatically split changesets spatially. The main reason is that the app is intended to be used on foot, maybe bike, mapping only a small area and doing all that on the ground where you actually are. So mapping from images or memory runs afoul of that intention anyway.

Granted, that still doesn't solve the case that you may have no connectivity and are basically forced to upload a big batch later. It annoys me a bit as well.

On the other hand, despite how angry the changeset comments may read, this isn't a big deal. Globe-spanning changesets happen all the time and yes, they do annoy local users trying to keep a watch on what happens, but the history on the OSM site isn't really well-suited for that either. Also, with enough other changes, those large changesets also fall out of the history range fairly quickly, except in places where no one maps anyway.