I don't see how that happens. What's to stop Iranians placing more mines in the water or launching drones to attack oil tankers?

Did you read what I wrote? I already laid it out. The US degrades the mines, mine laying vessels, and so on. Then the risk is reduced to a level that's acceptable for commercial shipping. That level isn't zero, despite what people say online. If you want a historical case study, look at the 1980s.