I loved the original Q and don't own a Switch, so personally I'm fine with it coming to 3DS (though I'd prefer vita even though at this point that's a pretty unreasonable request).
I feel like the issue here may be that Persona Q is mechanically moreso a spin off of Etrian Odyssey, which was specifically built to take advantage of the DS, and probably uses the same underlying engine and design philosophy. Both games heavily rely on using the bottom screen to draw maps, and while obviously it should be more than feasible to port that engine and set of mechanics to switch, I wouldn't be surprised if Atlus wants to focus on using the next Etrian Odyssey to test out bridging that gap first. It might require building an entirely new engine to make work.
All speculation of course, but I can understand how keeping it on 3DS was the logical conclusion they came to. Hope it gets ported someday though, the Q games are excellent and don't deserve to languish on old hardware.
