After a bath or shower, your ears are open to the air, and the water can evaporate. The earplugs keep the water sealed in your inner ear for a long time where

After a bath or shower, your ears are open to the air, and the water can evaporate. The earplugs keep the water sealed in your inner ear for a long time where it can't dry, increasing the chance of infection. Some people do just get more frequent ear infections than others, though, from swimming or even just daily showers/baths. That gets back to the luck/genetics thing.