I don't know enough about the current state of naval warfare but I've assumed this is related to the asymmetry that's emerged around protecting capital warships, especially in the scenario of a very narrow strait and a long enemy-controlled coastline. They can shoot relatively low-cost, short-range guided missiles from anywhere along the coast. Even if a warship stops the vast majority of them, only one has to get through to sink a multi-billion dollar ship that takes a decade to replace.
There are now similar asymmetries emerging across war-fighting and even though warships can still be effective (and less vulnerable) in other scenarios, this specific one seems especially bad. The other factor is that most of what ships carry through the straight isn't going directly to the U.S. so the impact on the U.S. is mostly secondary, reducing the risk the U.S. is willing to take. Of course, all this was known beforehand by military strategists which makes this all look even worse for the U.S. administration.