yeah i think the most logical reason is probably animation scene, if we are on mount our wol cant do the usual animation (surprise, point, etc) and some mount is huge so in cutscene or even in non cutscene (dialogue text) will feel weird.
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speaking of animation, after playing a lot of this day modern games, i just realized how out of date ff14 animation is compare to others. while graphic still can hold up to some point, i cant help but laugh everytime i see some animation occur when in cutscene.
for a fair point, their "single" animation is still good but if there is a context or scene where they need to chain string 2 or even 3 animation, some can end up hilarious in a way
the one that always get me is the "pointing" animation, the npc talk to you, turn around, point somewhere, turn back to you to say "lets go" only to turn again and start walking. really remind me of playstation RE animation, its so stiff.
then the most common one is when npc is running toward something (monster or an enemy) they stop just to play the "pointing" animation and when its over they start running again, in this day games these 2 animation could blend into one (running while pointing) but because the limitation they cant, and it always get me every time.
and the npc/wol reading book, paper or document. lift up their hand and stare into their palm hand, at least put a paper or something on their hand will ya?
nevertheless it become one the game charm i guess