Coz they are literal heat sink. Think of hairless skin patches on body like foot soles, palms and facial area that don't grow hair as heat sinks in machine that need to throw away extra heat. Body is never not burning calories and thus constantly creates heat which is also why balls are outside so sperm don't die of heat.
Tobirama4374 t1_j2d6vta wrote
Reply to ELI5: Why does putting one foot out from under the blankets bring so much relief of heat while laying in bed? by SirDuke6
Coz they are literal heat sink. Think of hairless skin patches on body like foot soles, palms and facial area that don't grow hair as heat sinks in machine that need to throw away extra heat. Body is never not burning calories and thus constantly creates heat which is also why balls are outside so sperm don't die of heat.