Because of the innate differences in the sexes that we recognize instinctively. Testosterone gives men rougher, thicker skins, so we equate a rougher, thicker, darker skin with masculinity and we consider it attractive if a man has this. But women generally have paler, thinner, smoother skin, without as much hair, so when we see a woman whose skin is a little rough and uneven we consider it less feminine and less attractive. Makeup covers evidence of uneven skin tone; it makes our skins look smooth, small-pored, ungreasy = youthful and feminine = attractive.
Also, as we age our lips get thinner, dryer, and paler, our eyes get smaller, and the fat pads in our faces shift or go away altogether. Male lips are thin and male eyes are small, so this process is okay for them; they're still masculine and attractive. When it happens to women they start looking less feminine, more masculine, thus less attractive. Makeup helps conceal these changes too.
Good answer.
If I dated any of those women and woke up in the morning with the picture on the left I would run for the hills. Most of the women I've been with have looked great without makeup and stunning with it. Your explanation makes sense.
Now you're scaring me into finding a younger woman!