Shrinkflation is real. Companies can only raise prices so much. If that fails to fulfill their profit goals, then they begin shrinking serving, giving them more dollars per weight or volume. Having said that, I have the insider knowledge to guarantee you that the quarter-pounder is and always has been 4 ounces pre-cooked. McDonald's does not want that false advertising suit. They did recently change their beef mix (lean : fat ratio) to a new recipe, which could account for a perceived change in size/volume.
Globally, Americans have always received larger portion sizes than the rest of the world. Hence the "land of plenty" and our notorious waistlines. In the 50s and 60s, a can of Coca-Cola was standardized at 6 ounces. Then 8 ounces in the 70s, 12 oz in the 80s, 16 in the 90s, and now 20-21oz is the standard. Productions costs had lowered, demand had increased, and the pop companies were reacting as consumers wanted. Restaurant servings are no different. Doggie bags are not common outside of the US.
From a public health and nutrition standpoint, this could be a good thing. I can spend a whole day in the practice and not see a single, attractive, non-staff individual come through. Pharmaceutical reps and physician liaisons are usually pretty hot, though. I try to steer business towards the hottest to keep them coming back. It's good to be the boss.