Why long-range anti-ship missiles do not finish as torpedoes

Why are there no long-range anti-ship missiles that make their terminal approach underwater like a torpedo?

A useful torpedo is already so heavy that the carrier missile becomes enormous, and the underwater phase adds far more drag than an airborne terminal attack.

A heavyweight torpedo such as Spearfish weighs roughly two tons. Giving a missile that payload and a substantial range would make the carrier missile very large. The underwater approach also encounters much greater drag than flight through air. Payload mass and the difference between those two environments therefore make the proposed weapon difficult to justify.