>>93516027>dimensional scissors seem to only work for opening portals to locations, not to people
They're not really clear on this but it seems like you just need to have an clear idea of where you want to go, and that can be "where X is."
Ludo has opened portals right next to Star, without any way of knowing her specific location, driven by his obsession with her and getting the wand.
With the opposite effect, when Star casually opens a portal to just toss Ludo away, it sends him to a void between worlds. She probably didn't have a specific location in mind, she was just tired of his shit and wanted him gone, so he ended up in "the abyss."
If Marco had followed after Star in the heat of the moment, with a strong feeling of somethign like "I need to see her again," he might have gone right to her.
But instead it seems like he made a reasoned decision to follow her some time later, and probably came to the realization that he doesn't know exactly where she is, but reasoned Butterfly Castle was his best bet and chose to go there.