Clothes were originally designed as ornamentation, after all, to increase your attractiveness by giving the illusion of muscle, by drawing attention to the face or crotch, and by adding color and contrast.
Without clothes, this soldier is homely and a bit too skinny. But the uniform gives him a square, stern face and a nicely tapered physique.
Here the black tie and sweater contrasts beautifully with the pale skin and reddish-blond hair. Nude, the paleness would be overwhelming.
After years of beefcake-watching, I'm quite sure what this guy is packing. It won't be impressive. But the bright-red, ribald t-shirt is a perfect counterpart to his expression of farmboy innocence.
With a sharp, severe face and sculpted physique, seeing what his penis looks like would be anticlimactic.
Keeping it hidden can be more erotic than openly displaying it. The mystery is half the fun. Hairy or smooth? Muscular or slim? Mortadella or Kielbasa?
Uniforms, symbols of status and authority, are especially flattering. This uniform accentuates the guy's chest and draws attention to his shoulders. Meanwhile his gun draws the eye downward to his rather impressive bulge.
Not particularly attractive with his shirt off. But the dark plaid shirt, open to reveal not a bare chest, as we expect, but another layer of clothing, gives him a pleasant mass, and adds definition and character to his face.
Clothes can hide minor flaws, like a small penis or a bit of chunkiness.
And major flaws, like this guy's shaved pubes, and the tattoos marring his chest, arms, and shoulders.
Clothed, we see only massiveness above and a bulge below.
Of course, some guys are perfect, clothed or naked.