Enchanting the shield makes the whole thing an eyesore and probably dangerous to use for epileptics (only half-joking here).
Plus the shield displaying no enchating effect would keep in line with the vanilla shield - which also does not have it. Probably for similar reasons.

That shield shouldn't be enchantable in the first place.

Welp. Right now it is enchantable via anvil with unbreaking and mending, like the regular shield.

That’s not supposed to be enchantable? I sort of assumed that was intended behavior. I suppose it makes sense that it is an accident, if you designed it by extending the vanilla shield.

I’m a bit curious about the enchanted effect, if that is just unintended behavior. It really is quite flashy, to the point that I thought it was designed that way.