I want to see the list of subscribers to a group that I created for the same reason I want to see who is following me on Mastodon: 1) so I have some idea who the people are who are interested in what this group produces, and I can steer content in the direction that's actually appreciated by the subscribers and 2) so I can invite people who I think should be in it, but aren't yet, and 3) so I can (potentially) preemptively block.

Re your point about privacy: I would think that if I create a group, and moderate it, I am the host of that group. I decide who gets to be in and who doesn't, just like IRL who gets to sit on my porch and who doesn't. Privacy does not really enter the picture here in my view.