Because the Navy won't pay to have new helicopters built for the Marine Corps... Is my guess.
The UH-1N is not really a cargo carrier, it's used as a command and control bird and a support gunship to support the AH
-46's are the Marines' version of the Army's UH-60s. All of the CH
-46's date from the Vietnam era and I don't think any of them are younger than 35 years. The Army UH-60's are much newer and I think are more capable.
-53's are equivalent to the Army's CH
-47's. I don't know anything about the CH
-47 to give you a comparison. Other than the CH
-53's are probably older than the Army's CH
-46's are the primary assault support bird for the Marines. Because of the size of the CH
-53, they can only get spotted aft in spots 8 or 9. Can't put them forward because they have no visual reference with the ship to land or takeoff safely (all they can see is the sea) and can't land them on the midship spots because there is insufficent rotor clearance with the superstructure.
So in terms of capability, it would be more advantageous to use a CH
-53 because of its greater capability, but in actual practice, it's limited to two per deck launch cycle, and there's normally only four in the squadron to choose from. There are more CH
-46's available so they are the primary workhorse aircraft and they can be launched from any of the spots. When they're loaded for bear for an actual mission however, they can't do vertical takeoffs. They have to do deck runs to get the translational lift to help get them in the air. So the CH
-46's spotted in the forward spots (1, 2, and 3) have to be light loaded so that they can do a vertical takeoff (as there is no deck left to do a deck run.) The midship and aft spotted (spots 4-8) CH
-46's can be max loaded for their deck run.
Operating from land they don't have this limitation of course.
But the one time we had an Army CH
-47 land on our deck, it was huge, easily taking up the space that a CH
-53 would take. I liked operating with the Army OH
-6 Loaches, we launched 9 of those suckers in the space we could launch 2 CH
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.