This is not an official answer, so I could be wrong.
- Easier to always increment than to control old/new/restored numbering.
- Progressive numbering avoids collisions with old instances/usernames/leftovers.
- Easier to read than a module_UUID.
- The instance name (on rootless instances) is also related to a Unix user and /home folder. With progressive numbering it’s less probable to cause collision (when removing an app, if all goes well everything is deleted, or almost everything, if something fails: leftovers…). User isolation.
Think of it like a key index on a db.
Although…