thats a bit simple semisimple! the money seized will no doubt be confiscated and vanish, so another ransom will have to be paid to the pirates. who might well be the same people anyway since somalia has no functioning government.
But the Somali argument -- from whatever government they have -- is that foreign companies encourage piracy by giving ransoms. If they stopped then it might decrease.
It's the same argument our government gives for refusing to negotiate for a ransom with kidnappers (although they do!)
Whether the policy is a sensible one or not I don't know. (I don't actually know if that's the case here or not, or if it's some other problem)