As others stated, it's because it's an ACN ability, and the reason ACN has it was to give a healing spell available for players that start in Limsa (given there is no dedicated healing class available in Limsa from the get-go until you unlock SCH).

Funnily enough, back in the old days when the cross-class system was still a thing, I remember going as SMN into Brayflox normal and having to take over healing because the actual healer for the party (a WHM) was still new and learning the ropes, and wasn't up to the task (she kept dying at the drop of a hat).

Needless to say we made it through that run somehow with me having to not only DPSing with my Egis/debuffing as normal but also spamming Physick over and over just to keep the tank alive as the WHM kept getting herself killed. I ended up with 3 commendations out of that.

Sadly that sort of thing is no longer possible with the loss of the cross-class system and heal potency now specifically controlled by MND boosts that SMN lacks.