Because the world is full of anthro Pokémon. You decided to rest up in a spa after a long day of work so you strip down your clothes and get into the sweaty smelling water.

To your right you see a big male Aggron sitting there with his eyes closed. He's so... hung... so... hairy... definitely a dad bod...

Aggron: Relaxing and sighing in relief. "Ahh~ That hits the spot~"