After the 1.16.0 update, the netherite armor was been added in minecraft, but the netherite material is only for the player's armor, and the horse armor didn't receive the netherite variant. in addition, after the 1.20 update, the armor trims was been added in minecraft, but the armor trims can only applied to the player's armor, the armor trims can't applied to horse armor.

I think they're bugs as these refers to the inconsistently issue.

My english is bad, sorry.