I don't think its totally a case of people not wanting being able to find someone they are happy with or wanting to stay in an unhappy marriage. The latter is probably more of a valid argument but I find it an unreasonable proposition that suddenly men and women themselves have changed in past 3 decades and are less compatable with each other then for the last I don't know how many thousands of years.

I think its to do with what people expect in life now that has changed and is having a knock on effect. I think the best way to describe this is it being a case of individualism on a society wide scale. Any rules that governed relationships or defined the role of men and women in society are being either being thrown out completely. The individual, be it a man or a woman, is now encouraged to look out for him/herself over the needs of society more than before.