The thing is, once some of the men I know who have been reluctant to commit have actually committed, I note with interest that thereafter they tend to be all enthusiastic about marriage and having kids!
The same men who were "not sure", are all "Mate it's the best thing I ever did", "My wife says..." etc and start getting all gooey and take an interest in friend's babies. It's like a switch has been flicked on and they are suddenly really enjoy the idea and the reality of being a DH and a father.
Of course, this is some, not all, men (although I have to say it describes a lot of men I know!)