Because despite what women say, social pressure still exists in dramatically large concentrations that forces men to view women as prizes. Their social market value is far higher than their male counterpart, a 5/10 woman is worth substantially more than a 5/10 man in the social setting. Because of this imbalance and the idea that men need to fulfil an unrealistic set of goals to be considered by a woman it creates a system of validation and approval for the man to play by, therefore he'll put any woman he sees above himself in terms of needs and wants...he'll view any interaction as a potential to get pussy and women are more than happy to play this game because they know that they don't need to put out at the end of it, so it's basically getting something for nothing for them.
Women can play guys on and get them to humiliate themselves and do nearly anything on the vague notion that they MIGHT get to stick their dick in her rotten and used up pussy, this allure is enough for the vast majority of men to utterly abandon their principles or self-interest.
Guys are also placed under pressure to 'please' his woman or any female he meets, he's seen as being in direct competition with any other remotely fuckable male that she knows, the reverse isn't true, a woman knows that any guy she's currently talking to would gladly travel through hell in order to catch a wiff of her rancid vagina and knows that provided she gives him just enough attention to keep him interested then he'll ignore other women (provided those other women aren't offering 'more'). Society has set her up to expect and demand near perfection from any potential suitors while also giving her a false sense of superiority over males that her the same as her in terms of looks, it has done the reverse for men.
As people say - Men tend to cheat because they just literally want to fuck someone different, they seldom put much emotional investment into an affair, they just wanted to try a different pussy for a change. Women tend to cheat because they feel like they deserve a better relationship, a better partner, better options, better sex, a better life...they cheat on both a physical and emotional level because real life doesn't live up to the expectations that society has given them, Men cheat because they look at all the work they put into a relationship, maintaining it and getting one is only validated with some bitching wet hole that's had 400 cocks in it before him, he cheats because he wants to be one of those "Oh those cocks were in the past" guys and not on the receiving end of it.
