But you don't see the US sending their army to protect those waters from pirates, now do we ;)
Actually there are some American, other NATO and even Russian ships patroling that area but It's not easy to localize small fast boats, which "pirates" use and after they already kidnap a ship then they have hostages, so any direct action is risky.
50 caliber Us government issued surlpus would keep the pirates away.
Yes but I heard that there are some regulations, which forbid the civilian ships to be armed.