They weren’t smaller than they are now in Dragonflight, they use to be taller demons/minions.
And since Tauren and Highmountain Tauren are the tallest playable races that can be Warlocks, may you, please, increase their size to the height of those races for every playable races?
The reason is to feel that we summoned a powerful demon to fight by our side, since they are the top demons for, at least, Demonology Warlocks, and they’re usually shown huge by NPCs.