Sex isn't why guys marry. If that was the force or pressure acting on men, they would never get married. Their family and friends put pressure on them. It's mimetic isomorphism since their friends are getting married. It's normative isomorphism since society encourages it. It's coercive isomorphism since their family wants to see grandchildren and constantly puts pressure on them as they grow older.
The reason guys "don't" want to get married, is because it means having sex with just one person for the rest of their lives. Not only one person who will grow older and let herself go, but his whole sex life will depend on her and only her, and that's something that he knows is more often abused that respected. Which means if she's angry, or not feeling up to it, he won't be having sex. It also means once kids come into the picture, no matter how much women want to pretend it's not the case to try and motivate men towards marriage, married men will tell you how shitty their sex life gets.