American do not want marriage and monogamy in the sense that women do.
Men do not automatically "adore" marriage. That takes time.
Men "adore" romance and the lover. When it is over, men can walk away and not think about it at all. That is why so many men will just walk out of a relationship without explanation.
We simply are not conditioned as are women, because we don't live in, and avoid as much as possible, the woman's world.
I think that a lot of marriages fail becuase we are transitioning into an economic monarchy. A persons position in life is mostly dependant on their parents position in life AND by how dedicated their parents are to them. Young people remain economically and emotionally more tied to their parents than they do to their spouses. Often times parents dominate their children's marraiges.
They view spousal relationships as being only for pleasure. Bonding between spouses is poor, and when the going gets tough - they bail.
In a healthy marraige, romance fades, sex becomes less than thrilling, but a deep bond of love, friendship and dedication forms. Unfortunately, in a society of selfish spoiled brats this doesn't happen.
What you describe is extended infantileism where people are unwilling to separate from parental support. There are reasons why animals in the wild abandon their young as soon as the young animals reach a stage where they can hunt on their own. Humans don't have that sense of obligation to the next generation. Soon we will have the first generation of human beings (if we haven't started already) whose parents are dying and who have never learned to survive on their own.