There can be a variety of reasons why married men might be on gay hookup sites. Some might be secretly gay and looking for a way to explore their sexuality, while others might be in heterosexual marriages that are unhappy and looking for a way to find some companionship and intimacy. Still others might be using the sites as a way to cheat on their wives. Whatever the reason, it's important to remember that doing anything like this can be risky and can lead to a lot of heartache and drama.