It’s simple physics. Matter is conserved, and you can’t have more then you’re given. How do we as creatures gain mass? By eating! These things don’t have a grocery store. I absolutely eat more than they do, so logically and scientifically my mass is greater. Them being taller just puts them at a greater disadvantage as they’re easier to move. A short person weighing 100 pounds is harder to carry then a tall person weighing 100 pounds.

If they get supernatural devil powers, then I get to say special prayers and seek refuge in God’s protection against their sorcery. This is hypothetical, so we can assume this would work, because these curses defy our reality’s laws so that guarantees the existence of an omnipotent creator capable of protecting me from evil like that.