why does lunch differ in different parts of the world?

It's called culture. We all have one. Food is a big part of human culture because it's essential to life (no you won't die without rice, but why pass it up when it is so versatile and so good). This is why "rituals" have occurred around food. The American ritual is to process food until it's so soft and weakened that we can down it within a few minutes while paying no attention to what we eat. The majority is also overweight here because of this. Not to mention the amount of heart burn, indigestion, etc. But, it's how our food ritual goes. It's hard to find others who like me not only "love to eat" but love to enjoy the process of cooking, eating, and each others company rather than shoving burgers down their throats. We're supposed to chew our food, people... What you call crude seems to be misused adjectives. American lunches are crude. They are messy, disgusting, often very bad for you, and a lot of people here barely know how to chew with mouths closed, use a knife and fork properly, not to mention avoid slurping their drinks. Treating food with respect is important.

Rice is a healthy food to eat but you wont die from not eating it. I dont see why the big deal with meal times anyway. I visit my family on weekend and have sunday dinners but we never really had ritualistic meal times. Its obsurd if you ask me.