Is it really all the guys, or is that a hyperbole? In any case, it happens either because they have very questionable taste in women/guys, or ... nope, that's it. Just my opinonion, anyways. I have a near-zero tolerance for cheating. I value loyality, honor, respect, and love.

Thinking about it, I suppose there are a few other reasons. Someone may be in an abusive relationship, for example, and not know how to "get away" then get close to someone else.

Another situation might be a drunken antic, but I honestly have been drunk plenty of times and never jumped another woman, or any woman for that matter. I guess some people are less in control when intoxicated? I'unno. Frankly, I try not to put myself in such a situation in the first place; in other words, not drink with someone with whom I have a mutual attraction that could result in an oopsiekiss or worse.

The only other thing I can think of is a relationship with terrible communication and a complete misalignment of desires and goals, causing both people to be with each other, despite not really caring about or putting much of anything into it.

Beyond that, I dunno.

It could also be that they're trying to indicate distrust and/or fear of a repeat scenario.