The entity item_display will not show the proper skin of a player_head when you try to summon it or modify its data using SkullOwner:{Id:[I;0,0,0,0]}, with of course replacing the [I;0,0,0,0] with a player's UUID, and instead just shows one of the default skins.

If you summon the item_display of a player_head using SkullOwner:"playername" then the proper skin shows on the item_display.