This works for some folks. But it turns out for many that what you eat matters, and managing hunger/cravings is a big part of the battle, and that there are easier ways of dropping pounds that don't require calorie counting.
Yes, no question that portion sizes have mushroomed along with the obesity epidemic, and people get used to eating these massive portions. It's cheap, so the more you get, the more you eat - god forbid any of it should go to waste!
Yes, US folks in general eat way too much. How to get them to eat better? That's the challenge. And it doesn't help that they've been getting poor dietary advice for decades, that healthy food is expensive and usually requires more preparation, and that unhealthy food is cheap, abundant, and very convenient. Just a run through the drive through on the way home!