Except the utility a common unit helicopter like the Blackhawk, which most US ships have room for two*, has such benefits in so many ways it out weights the done sides.
Especially since while the US ships OFTEN operate in concert with a CSG they just as often F off to do lone wolf stuff.
Remember the Burke was design WITHOUT any ability to have helicopters outside of a pad originally.
That was considered such a stupid set up by the fleet proper that they redesign the class to have a hanger set post haste. Despite having the same exact reasoning you have here for lacking then.
And from the looks of it, other nations agree with this getting similar size copters when possible with two spots.
*Like the only ships that don't have space for two S60 type are the old minesweepers, the Freedoms, and drone boats. The rest have space for and do get 2 SH60 types unless they are in port or have a mission they don't need 2 for. The aircraft doctrine is very flexible in the USN for this exact reason, with the Ship and it airwing being two different entities that can be switch around the fleet as needed.