>>29419368When pondering about why a pokemon doesn't learn move X, don't look at the english name, look at the Japanese name. (Example: Aerial Ace)
Raichu not learning "Tail Glow" might be strange, but Raichu not learning "Firefly Light" isn't all that strange, given how Raichu doesn't have anything in common with fireflies, nor is it Manaphy.
Though Manaphy makes me wonder why Lanturn doesn't learn Tail Glow, one could think the same explanation [as Manaphy's] could be used. Or maybe I just am forgetting something.