The coastline of Iran makes it so that they can fire missiles and place mines in a way that’s very hard to stop without actually placing troops on the ground to clear the coast. It’s not something we can realistically achieve just by bombing.
Sea mines are very inexpensive to deploy - they can use small civilian boats to place them. We know they have many of these mines and the coastline of Iran makes it very hard to stop before they are placed. It’s not something they need some massive navy ship to deploy.
There were less than 8 million babies born in China (and it’s dropping every year) - so like every single pregnant Chinese woman would have to come to the U.S. and give birth for like 30 years for this to actually happen?