First I would like to open that the statitstics dealing with sex factors in infidelity is getting pretty close to dead even, so the especially men addition isn't especially tru.
As far as the rampent infidelities in this day, I beleive that is part of our training given by society.
We live in a temporary world, where everything seems to be viewed as disposable and replaceable.
Everything we ecounter on a daiy basis is based on how it can bring joy to a person and then be cast away with out a second thought.
Fast food, plastic/fibreglass cars, CD's (weakest musical format ever), MP3's (dont even exist in the physical world, so no worries about losing or breaking), and a whole plethera of cheap chinese made crap we know won't last till the end of the week.
We are a society that, as a whole, shuns anything long term or substantial. This naturally leads to an attitude of impermanence that permeates all apsects of our society, even our relationships.
Factor in that our culture places such emphasis on "players" and also that stigma's against women playing the field have dropped alot, and we have a giant clusterf*@K of free love going on.
As is always the case with Humankind, we are ultimately the source of our own problems.