This works out to 12+ releases annually, not counting beta and test releases (more on those later).
Android apps need to be able to save their state and restart where they left off at any time.
For an #OpenStreetMap editor this is rather painful as there is a lot of state and some functionality changes require adding or changing what we save. While it would be nice to be to migrate seamlessly between versions, it is currently not feasible. That's why we only change this for major versions.
Maintenance/patch versions are typically made available once per month, with the exception of months with major/minor releases.
The patch releases typically contain updates to the default preset and imagery layer configuration. Both of these can be updated manually without an update, but that increases the amount of phoning home and simply updating the app avoids that.