Personally I've been putting it down to geographical separation. Ifrit was the first primal summoned in mainland Aldenard and tempers everyone and their mongoose. Because of this he would be the first primal most Eorzeans think of, so when they think of "tempering" they think of Ifrit tempering. This would also of course spread to Vylbrand, but wouldn't gain as much traction there because the island already has experience with a primal who has been tempering people (assuming he did this the previous times he was summoned and drowning isn't recent tactic). Why use a different term when you already have one? The other primals may have specific terms for it (like touched which may just be what the Syplhs call it instead of pertaining specifically to Ramuh), but as Ifrit and Leviathan are the most prolific temperers their terms would be the most used.