I had a thought recently, Vriska, Aranea, and Meenah are the only trolls that seem to have a singular self in the dream bubbles. My theory is that it has something to do with going god tier. We see other trolls who have gone godtier in the dream bubbles, but only these three gals did so in the "canon" timeline. The exception is of course, Aradia, who has gone godtier in the "canon" timeline, but still has Aradiabots floating around Maybe it's because she isn't dead, and intends to stay that way?

There’s actually multiple Araneas and Meenahs in the Bubbles.

If God Tier in the Alpha Timeline invalidated the Ghosting, Jadesprite’s ghost, John after killing Typheus and Throat-slit Doomed Dave wouldn’t have been in the Bubbles before LE blew them up. Vriska, however, only has one ghost- (Vriska), while Gamzee has shown to have zero Ghosts at all, yet he did die in at least one Timeline.

My current working theory is that of Canon Divergence- Ghosts show the paths people could’ve taken, different developments, each iteration of a Ghost in the Bubbles is pretty much representative of a notable divergence in personality and character from the ‘Alpha’ version. As such, Gamzee and Vriska, as well as, Caliborn, would make sense to have no Ghosts at all, except for Vriska, whose ‘Alpha’ died before the Alpha was retconned.