What? They're not stripped from players that earned them and sold back to them.
The event for them happens, they're obtainable, then after the event ends, they're either brought back a few years later (as with the FFXV event that is returning in September) or they're put on the shop for people who missed out. Not ideal, but it beats them never being available ingame.
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It does answer it. You just don't like the answer. Cope.
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Yeah, FFXIV definitely has fewer mounts. But it also doesn't exist for as long. One thing they really ought to do is some mount dye system, because while it's good that almost every new mount they release is unique (at least in the sense of not being a recolor) some people might really want to have said new mount in red, or green. Idk.