Your bladder can’t take so much
Everyone’s body is different, and most of us have bladders that can’t take so much. Adults can roughly take 16 ounces (2 cups of water), and kids can take 4 ounces only.
Your bladder is basically a muscle, and when it is overworked, it will affect other things like your pelvic floor, which is the muscle that “decides” if you should pee or not. So, it is best to listen to it before it starts deciding otherwise.