That's because it is moving very fast, like a bullet. If you throw a bullet at someone it doesn't do much damage. It does rather more when you fire it from a gun.An improvised weapon does 1d4 when used by a character, you catapult that same chair or broom or pot and it does 3d8.
Indeed. So no grapple. A catapulted net does damage and NOTHING ELSE.Catapult is a magic spell, the wording in the spell bypasses the physical and logical constraints to implement the effect noted and only the effect noted.