[ihatehn]

Every version of Organic Maps and CoMaps (and probably to some extent OsmAnd) use slightly different formats of maps; consider a new feature to support park bench backrests/colors/materials. That info likely wouldn't have been in the map files before for efficiency, and now it needs to be. But any given other app may not have that feature at all, and instead decides to save space and bandwidth by compressing the files instead. And a third app might improve performance on old devices by preprocessing routes and storing them in a new format in the map data.

So you can see the work of keeping map files cross-compatible would either hamper the release of new features, or take a bunch of work, all to save a few hundred MB on people's phones