Because we are imperfect animals with imperfect survival mechanisms, and sometimes water is actually hot enough to heat your body above what it considers to be its threshold for thermostatic equillibrium.
Problem: Body Temp Too Hot.
Solution: Emit Salt Water Tears from basically all of your skin so that the heat can transfer into Salty Tears and then evaporate. Works very well in low humidity situations.
But also problem: Humidity and temperature in ambient environment is so high that evaporation either does not work at all or is ineffective at dissipating internal body temp to the outside environment.
Same Solution: Keep sweating even though it doesn’t work, enjoy heat exhaustion/stroke.
This is the whole problem of a ‘wet bulb’ temperature causing mass heat exhaustion, stroke or death: If the humidity and temperature are high enough, long enough, its literally impossible for a human body to naturally cool down.