Under way, they leave telltale wakes which extend for several ship lengths behind them making them even easier to spot with the naked eye or satellite sensors. Advanced electro-optical and signal analysis sensors make this task much quicker. Anti-ship missiles hold surface ships hostage, just like Iraqi tanks were hostages of airpower during Desert Storm. Like tanks, ships use the concept of maneuver to gain an advantage over the opponent. But at sea, there is nothing to hide behind.
Ships are capital intensive and filled with expensive people.
If a ship makes a mistake, a nation loses an expensive asset and many sons and daughters. During the Persian Gulf Oil Crisis, as the US Navy escorted oil tankers through the area, they relied on helicopter and aircraft support to extend the eyes of the ship over the horizon. Any fast patrol boat headed toward the convoy would be known well in advance. Since patrol boats have limited or no anti-aircraft defense, they are easy targets for aircraft. Ships with more extensive defenses are still at a significant disadvantage.