All the things a woman has of value that draws men to them depreciates as she gets older. Youthful look, fertility (by 30 a woman has lost 90% of all her eggs), minimal mental/psychological scars, gusto for life, no kids and being malleable. All these thing get progressively less as a woman proceeds to menopause.
Meanwhile, assuming a guy is not lazy and works on himself. He has higher status, money even if his looks has taken a nose dive (women only care about a combination of 3 things from men: 1. Looks (height and/or face) 2. Money 3. Social status). So why should a man therefore who is of more value later in life settle for a woman of lower value than him?