They're afraid of coming across like neck-breathing perverts, like Lord Saletan does here. The thing is, there's actually a point to be made about how our culture is very pious about sex and pregnancy, and the only way to maintain that piety is for the young women of the country who are emblems of purity to the public to have very private access to the symbols of sluttitude: abortion and birth control. But the way he goes about it screams of neck-breathing perversion, making a list of daughters of candidates between the arbitrary ages of 17 and 30. It's actually indistinguishable from a list made by perverts of "chicks I'd like to fuck", with the lines drawn to communicate to other men that you're both properly contemptuous of women aging and a little (but not too edgy) with your willingness to objectify teenagers. Does Saletan think that women over 30 can't get pregnant and require abortion services? Does he think that your willingness to have sex (or men's willingness to have sex with you) shuts down at 30? We can only assume.
By the way, this is all the funnier to me personally because it's my 31st birthday. Glad to know that I'm officially out of Saletan's danger zone. I feel much better knowing that if I ever meet him, I'm in the "hands-off" category.