Underwear offers a barrier that keeps residual urine and feces particals from absorbing directly into your pants.
People that dont wear underwear let their bodily fluids make direct contact with their pants, and then expose them directly to any surfaces their bits might touch.
Not wearing underwear is unhygienic.
I see posts like OPs, and hear people saying such things IRL, and I always think, “This person would straight die in a week if they faced the most minimal survival situation.”