For me, it's mainly because of Communitas -> Community Balance Patch -> Vox Populi (rebrandings and changing devs over the many years) it's what makes Civ V really worth playing (Windows-only because the SDK was only released for the windows Civ version). Far superior AI, balance and more features.
But also because Civ VI feels like it's much more combat focused.
But also because Civ VI feels like it's much more combat focused.