Manufacturers and retailers end goal is to increase profit and unfortunately serving size is something that helps drive profit.
The coffee shop I love changed their drink sizes a few years ago. Small had been 8oz. became 12oz. Medium which had been 12oz. became 16oz. Large had been 16oz. became 20oz. The first few weeks of the change I would order a Large when I meant to order a Medium. It took deliberate effort to remember to order the right size.
Along with this the price increase was strategically set to have the largest price be the "best value" (like Movie Theater Popcorn).
I doubt anyone took a calculator and estimated how much fatter this change would make the customers.
To put it in perspective, I looked up the nutritional info of the nation's largest coffee chain and their 20 oz. Mocha with whole milk and whip cream has 90 calories more than their 16 oz version.
That 90 calorie increase adds up: order the new large 5 days a week that would be 450 calories more a week or 23,400 calories more over the course of a year. Over the course of a year this could be 6 extra pounds, over the course of 10 years, that one change could add 60 pounds.
Small changes over time add up. This is true as it increases the scale, it is also true as you make slightly better choices and watch the scale descend.
The next time someone gives you a serving of food, slow down and think about how much of it is your personal serving size. This is something that should change day to day dependent on what you are craving and how hungry you are.
Tonight, after a long day of projects the idea of cooking just wasn't on the table. We ordered a medium pizza with light cheese, pepperoni, black olives, mushrooms and onions. I made myself a salad as my main dish, had my one slice of pizza slowly and ate another large bowl of salad (mixed greens, kidney beans, and a splash of balsamic vinegar without oil) to feel satisfied to the point where I didn't want a second slice. This is helping me reach my new current goal of seeing 149.