Does it make sense to you that you can't carry on a bottle of conditioner, hand cream, water or soda (over 3 oz) on a plane but yet you are allowed to carry on a small knife?
Liquids are easily disguised as harmless while they can really be volatile substances, ready to explode at any moment or when another “harmless” agent is slipped into the bottle. Knives are knives. You can’t exactly disguise them as something else and then suddenly pull them out and start stabbing people.