Why not? Many MMOs have some manner of "direct binding", where you can choose to bind an action rather than a matrix space (X button of Y hotbar). It's useful for keeping the most common binds in comfortable locations while having what you most need to track (but not necessarily hit often) in the most visible locations.
I'd go one further, though -- Retained Mod States option: held keys remain in the mod state they were first pressed in. Sounds obscure but it's literally the difference between having easy access to Shift/Alt/Ctrl QWEASD, all prime real estate, where you would otherwise have your movement cancelled mid-hold by hitting any of those mod keys. MMOs that allow for that can generally have many more skills than XIV without seeming to suffer from an overwhelming number of buttons, just because they still aren't spread any further or any more uncomfortably.
...That's literally the opposite of direct binding. That's "matrix-" or "space-" binding, as just described. And as every hotbar's binds, shared or job-specific, are mutually exclusive with one another, it would be incredibly limiting, where direct binding is not.
Direct Binding = mouse over the skill in Actions & Traits menu, right click or config command -> Bind, hit bind key. Now place it wherever you like and the hotkey is still shown as what you've bound it to. Where a conflict exists, you are thus informed and can either separate them by conditionals, e.g. "In combat", "Mounted", etc. or by rebounding the previous holder of that keybind. You can now move your bars about however you like for visual convenience without messing with muscle memory or even skip placing skills that you have no need to track on your hotbars without losing access to them. It's a simple enough system and while it might not significantly benefit that many people, it's nice enough to have.