The Red Sea and Persian Gulf are nearly land-locked bathtubs - ships would lack ability to maneuver. It could be a shooting gallery for anti-ship missiles.
The Axis of Resistance doesn't need to win any battles or wars ... they just need to inflict 1,000 painful and emasculating cuts to the West.
There's also the risk that if there is a large US footprint in the area, other regional Islamist movements may see an opportunity to attack American assets and personnel to raise their international profiles and their local recruitment. Islamist Somali pirates in the Gulf of Aden come to mind.