I think the issue is mostly that there isn't a real clear way to label something PRIVATE without it being in the actual Title itself. Which would then just make the RP look messy and cluttered.
Even if it's in the sypnosis as one of the first things roleplayers read, or in the summary, or in the tags, or in an OOC thread--which I stopped posting those kinds of things because they weren't necessary when it's just me and one other person who write--it's like roleplayers get excited because they see the type of UNIVERSE that it is, and it immediately intrigues them.
For example, the Pokemon universe I have with my co-writer. It has PRIVATE labeled in just about every way. It's in all three places that are clear to see, even in the sypnosis, but people either read over it, or just don't like paying attention. My RP partner and I have used this site for years for a lot of our roleplays because it's familiar and one of the better laid out roleplay sites.
I think with PRIVATE roleplays, they should have a function that is similar to the one that has OPEN characters, or REQUIRE APPROVAL when a new Universe is being made. That way it limits the amount of spam character sheets, and the only people who are allowed to submit characters would be the GM and the co-GM. My only hesitance on something like that, though, is that I have had experience in the past that adding a co-GM is not always functional. For one RP, I was able to add my writing partner as a co-GM, but for another RP, I was not able to.
From my understanding, it was because RPG was going through a glitch at the time, but I still CANNOT add my writing partner to that RP as a co-GM. Not that it's of any use, now, because that RP universe is currently closed. But having an option to whether or not allow an RP to be OPEN or PRIVATE should be at least a thought.
I know RPG has gone through so many design changes, and changes in general, and it's ever evolving, and some things have become easier, however; I think GM's should have more authority and control over their own universes. I'm not saying make it like an admin-level authority, but giving a GM the option to reject characters completely from their universes should be something they can do so that it keeps their universe clean and easier to navigate. Especially for those who like cleaner looking roleplays.
And from the state of most RP's--the ones that I've noticed at least--it's not so much as writers are leaving and spots are opening up. It's that GM's of other roleplays are barely getting theirs off the ground before disappearing. That's another issue that I won't go into because I no longer participate in open roleplays like that, but still, it's almost the same concept. Having characters in limbo just in case a spot opens up is ineffectual and doesn't really serve a purpose. If a GM decides that they only want 8 roleplayers, and choose 8, then the other 5 that may have been submitted should be able to be deleted, and the actual number of characters should be present. So instead of it saying 13, it'll say 8.
It might seem like we're being nit-picky, but it gives a more accurate representation of how many characters are actually part of the story/roleplay who have stories to follow.
As a long-time member of this site, I know things are constantly changing, but maybe one of those things should be how Universes can and should be labeled. If it's not part of the Multiverse, any GM should have more control over their own roleplay--even if it's based off of something like pokemon--they should have a little more control over it.
It might just be my biased opinion.