I don't think it's a matter of it being harder to stay married or easier to get a divorce. I believe it's about having more options especially for women. In generations gone by women were more dependent on their husbands financially. This was especially true of the "Leave it to Beaver" era. When these women had kids they were pretty much put in a postion where they were forced to put with things they may not have liked from their husbands. A lot of women stayed in bad marriages for financial reasons. Other women dealt with infidelity by looking the other way and saying such things, "As men will be men."
Today there is much more career and income opportunity for women and they are less inclined to accept or put up with the things their grand-mothers or great-grand mothers did. A recent study stated that (women initiate 66% of all divorces in America). That is 2/3rds! I wrote a hub about this quite awhile back.
Unhappily married men are far more likely to cheat then run to the courthouse and file for a divorce. Even mistresses are warned by their friends that "married men rarely leave their wives". The more options women have the less crap they will put up with! Each of us is entitled to have our own "deal breakers" and no one is "stuck" with anyone.
Essentially a divorce is nothing more than one or both people coming to the realization that a "mistake" was made. Maybe we'd all be better off if pre-marital counseling was mandatory. I suspect the number one reason for divorce is and always has been (selecting the wrong mate). When most people take their vows they assume they will be sticking together to take on whatever comes their way but (no one thinks it will be their own mate who will be attacking the marriage). Once you realize your spouse has a different agenda than you or no longer shares the same goals for the union then the marriage is over. Staying together for the wrong reasons is just as bad as getting married for the wrong reasons.