[This post will be quite long and delves into philosophy talk, but it is a theory I had, so bear with me...]
Plato's Allegory of the Cave is a very simple but very profound short hypothetical story that goes as follows:
Imagine there were people who lived in a cave and all they knew about the cave were the shadows on the cave walls that are projected via an unseen fire. The people in the cave are chained up and cannot move or look behind them to see the source of the fire, and they cannot see the people who move objects in front of the fire that create the shadows in the first place. Their whole world view, culture, and way of life is built purely from the scant knowledge they gain from the shadows in front of them.
Now imagine you tried to take one of these people from the cave and show them the reality behind everything. What would happen? Because the prisoner in the cave has never seen the fire before it would hurt his eyes and he'd probably try to look away from it, and shun it even though it's the thing that makes the shadows. But eventually, after some time he'd be able to observe the truth behind the cave and the shadows. And not just that, he'd be able to see other things about the world entirely like the moon, sun, and stars.
He'd probably return to the cave to try and tell others about the incredible things he saw. But would any of them believe him? Their whole world view is just the cave and the shadows, they don't know anything else and can't possibly imagine any of the things he's describing. And even if he took them from the cave would they still come to the same conclusions? Would they even believe him about what's outside?
And returning to the cave once you've seen the truth seems cruel, because the man now knows too much. His eyes have accustomed to the light outside the cave, so seeing in the dark is impossible for him where as the rest of the prisoners are able to see just fine as they've only grown up in pitch darkness. This would just further convince them that leaving the cave is a bad idea, and that leaving the cave is what lead to this man becoming "wrong" or injured in some way, even though there's really nothing wrong with him at all.
Now that I've explained the hypothetical to you, I want you to remember what Ult!Dirk said about the Candy timeline and how he basically holds a lot of disdain towards the very idea of being stuck in a "worthless" world. Dirk has ascended to the point where he's aware of how everything works; he has merged with all of his alternate selves across every known possibility and timeline, and thus has power over the greater narrative. He's even aware of "us" the readers, and knows that the world he lives in only persists because people find it entertaining.
Even though it is canon that Dirk finds the Candy timeline to be worthless, I will posit the idea that he also thinks the same of Meat, and thinks that both timelines are in a way "The Cave".
Dirk has taken two people from both Timelines whom he trusts and admires deeply, but left everyone else behind. And not only did he leave them behind, but he's just going to make a new game session entirely. Dirk has already succeeded in just escaping the "worthless" reality where nothing is canon by killing himself, so why does he even want to hold this new session where everyone can escape irrelevancy together? If everything in that other reality doesn't matter, there's no point in even wanting to keep those irrelevant extras around at all, is there?
Unless, of course, he wants everyone to leave the cave.
I think Dirk wants all of them to merge just like he did into one conglomerate being so they can finally see and understand what he does about this whole world, which is why he just killed himself in one reality but then helped Dave and Rose ascend. But, I think he is picking and choosing personally which halves he thinks will be desirable enough to keep around, basically, which half wins that inner battle.
Think about it, he chose Meat!Rose to ascend, but not Candy!Rose. And he did the opposite for Dave, so why is that? By choosing two variations from two different contrasting realities that are in direct conflict with one another, he's kind of connecting them in a way because he's bringing those two together in one new session. The rest of the cast don't have to really worry about having an infinite number of "potential" other halves either, because those other halves were literally destroyed by Lord English or the Green Sun's massive black hole explosion. So, technically, right now there should really only be two "canon" (however you want to call it) halves for our alive cast of characters.
Leaving the cave in this instance would mean being ready to actually enter the new session and participate, in my opinion. But I don't think it will really work out in this horrible ideal way lol. The hypothetical also talked about how the prisoners who didn't leave the cave recoiled at the very idea of what leaving the cave does to you. I doubt any of them would WANT to ascend to some Ult!Self, if they saw Rosebot or Davebot, or even just learned about the things Dirk has done.
I have other theories, but really this long post was just about how The Meat and Candy timelines connect with this ancient ye-old hypothetical.
