It's an interesting stat and it would be interesting to know all the why's and wherefore's of it.
I'd guess that a degree of greater financial independence allows women to instigate divorce now where they couldn't have before. Also, the loosening of religious ties in most communities would mean less people frowning at you for not being a good little wife in the face of whatever it is that tests you.
In that death via domestic violence is more than three times as likely for a female than a male and 1:4 women experience DV but only 1:6 men, it could be that more women seek divorce as they are physically or mentally bullied more frequently. Education programmes and law changes mean they can now get out of an abusive relationship where once they couldn't. So it might not be that men simply 'didn't see it coming', rather they may not have realised the little lady would do something about it.
Similarly, it may be that men had affairs and women weren't prepared to put up with it.
But that's all conjecture, the reasons cited for seeking divorce could be more interesting. It could be that yes, the men did not notice that sleeping around and hitting the kids and not coming home until pissed did indeed have an unexpected result on the marriage that the man hadn't considered as women think differently.
If the reason most commonly cited by women for divorce is 'I found somebody richer and younger and fitter' then my argument is potentially weakened.