My concern is hypothetical so far. Imagine a malicious troll starts posting garbage (CSAM, calls for violence, whatever) in a community with an absentee mod. The posts show up on everyone’s All feed. You can report the posts, but without an active community moderator the posts will stay up until the instance admin notices and takes action. Having more mods, and mods who are active users, increases the chance that garbage gets taken down in a timely manner.