Imagine if in oblivion you could have fortify magicka health fatigue, fortify all stats and attributes and feather on all pieces of armour ... isnta-god mode and would not be fair
Not so, it is the same principal as enchanting wepons. You are always limited to the strength of your soul gem (max 1600 Gand soul gem with grand level soul). Which does mean that you can have one super enchantment or maltiple weaker enchantments.