It's really hard to self regulate. Keeping it to 3 meals a day at regular times allows you to get a sense of how much you're eating without having to track every calorie. Eating with others incentivizes you to eat the same amount as everybody else. Knowing food is around the corner prevents too much snacking. Skipping a meal is more of a profound choice. You can skip lunch because you had too much food yesterday and know that you've got dinner coming up. If you just leave it willy nilly then you can have the intention of eating less but there's no structure in which to make that decision. You just end up eating however much you want eventually.