I'll have to look into this. My immediate assumption is that we don't want member systems overlapping, which could happen if the member system is on a Composr level (rather than Conversr) and someone chooses to use a different forum driver (e.g. PHPBB) which also has a member system.

By keeping the member system within Conversr, this ensures Composr doesn't have two member systems (because when picking another forum, Composr will use that instead of Conversr).

I have no plans to change this functionality at this time without a very good reason as it would require a lot of core modifications. As a workaround, admins can install Conversr but hide / disable all of the forum aspects of it and just use members. This is what I do on one of my sites.

While Conversr refers to our Member/Forum system, you can already remove the cns_forum addon leaving just the member system. If you then want this to integrate with another member system without actually using a forum driver, there are the user_simple_spreadsheet_sync and user_sync non-bundled addons that allow programmers to setup batch jobs to keep these systems in sync.