There can be two reasons for this:
- You cannot promote yourself to community admin while in moderator mode, as you already have those permissions. Essentially, you're seen as an admin when you're in moderator mode.
- The permissions in a community are linked to hierarchies within the company. Not all users with permission to access moderator mode can also make decisions in individual communities.
If you want to become an admin in a community, please contact one of the existing community admins for assistance.