[swores]

Is it worse than having a bath where your ears go under water or a shower where water splashes into ears? Isn't that something many people do daily?

[ketzo]

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.

[sokoloff]

Diving has total saturation and additional pressure driving the water deeper than water splashed at 1 atmosphere of absolute pressure.

Combat (or riding or flying) has longer duration of dampness than getting out of a bath/shower and going about your normal routine.