Monster Lightning Bolt Question

I would guess the reason is that Weapon/Monsterattack pointers are shorter, so therefore can be manipulated into pointing to the longer Spell Animation data. It's notable that if you use some nonstandard Weapon codes, you will get partial frames of Spell Animations. I know that Meeple used a lot of these for his weapons in Meeple Fantasy 6 for some interesting effects.
I don't think it works the other way around though? At least, I haven't found a way to make Spell Animations display Weapon strikes or Monster attacks.