What protects from cold also protects from heat. Insulation goes both ways. Your natural body temp is lower than 100F and if humidity is compromising evaporative cooling that sweat would give you… It’s better to insulate yourself from the heat. Also sun is bad.
We basically run on tiny combustion engines. Exothermic reactions.
We aren’t a passive 98 degrees, we would be hotter if it wasn’t cool enough outside. Higher heat would cause different cellular structures to become misshapen, leading to system breakdown. I’d be like trying to run a cpu cooling loop with boiling water.