The small number of successful pirate attacks, an increase in military patrols, and legal concerns have kept many firms from hiring security.
Less than half a percent of the ships that transit the Gulf of Aden are attacked by pirates, and of those attacks, less than half are successful.
That statistic, reported during a Senate panel Tuesday in Washington, offers one reason why shipping firms have been unenthusiastic about using armed guards to thwart pirate attacks, leaving the problem to be solved by the US and other militaries.
"Many in the merchant shipping industry continue to assume, unrealistically, that military forces will always be present to intervene if pirates attack. As a result, many have so far been unwilling to invest adequately in basic security measures that would render their ships far less vulnerable," said Michele Flournoy, the Pentagon's chief of policy, at the hearing.
As with the "asymmetrical threat" posed by insurgents on the ground in Iraq and Afghanistan, experts have been taken aback by how quickly a small band of pirates can successfully attack large vessels with millions of dollars worth of cargo aboard. One answer is for shippers to provide for their own security, employing armed security crews to man each ship.
But those crews can be expensive and the shippers don't necessarily want to spend the money to hire them. And despite the recent high-profile pirate attacks, shippers recognize the odds are in their own favor and essentially see any ransom they may have to pay as the cost of doing business.
About 33,000 ships sail through the Gulf of Aden each year, and there were just 122 attacks in 2008, according to Pentagon officials at Tuesday's congressional hearing. Of those attacks, only 42 were successful.