The US does not have enough servicing ships to keep US fighting ships supplied. This was okay when the US operated near land bases, but with Iranian missiles and drones making many US bases unusable, the US has trouble keeping its ships supplied.
The US does not have enough military ships either because the ships need time for repairs and the crews need time off, so the navy actually needs an extra ship or two for every two in military operations. While two are doing operations, one is in repairs and rest. War-level operations, including blockade, are 24/7 work that degrades sailors’ capabilities without rest.