The Freedom of Moonkin vs The Limits of Metamorphosis

[Dromerd]

So I was brainstorming today about shapeshifting in the game overall, and I can't piece these things together.
I'm asking the devs for help/answers.

When I enter Moonkin form, I can cast almost every kind of spells and abilities except healing spells. Holy, Shadow, Fire, Frost, Arcane, Nature spells/abilities, even Physical and Ranged ones too.
But when it comes to Metamorphosis, I can only use Fire and Shadow spells/abilities.
(When I mention Metamorphosis, I consider the form with the use of Demonic Influence LRE, since I need that to use the ability non-stop. Reduced armor/damage buff.)

Both forms are similar to eachother. Increasing armor and damage, yet one has a serious limitation.

Why does one have a limitation while the other doesn't?

If Hunter Chicken exists, why wouldn't Frost Demon be also possible?

(Just a little extra: I can use Paladin Holy Spells in Shadowform but not Priest Holy Spells.
Again, if either works why wouldn't the other too?)

I would assume that the Demon theme is around Shadow and Fire, but this wouldn't matter anymore because this server advertises free choices and no limitations.
Also happened to see someone with an Iceflame Overfiend today.
So the Demon theme can't be a reasoning here.
Even in the Warcraft lore, there is Lothraxion. A dreadlord infused with the Light. Holy Demon/Healer Demon could be also possible but this topic is not about new ideas.

My other guess is technical reasons, which i don't know much about. In which case it would be kind of disappointing, but it is what it is.

I would appreciate if anyone from the dev team could explain this to me.

[Dromerd]

@Dromerd Posted a week ago and still no replies?
Working as intended, I guess.
There goes the freedom of creating whatever you want.