Actually, that's something I can comment on a little. That particular custom is an outgrowth of the unspoken attitude of "American Bounty". Compared to many parts of the world, food (particularly meat, which is resource intensive and therefore far less common in undeveloped countries) is relatively inexpensive here, and large portions are part of our cultural heritage.I was surprised by the portion sizes in LA
You can see echoes of that in other cultures around the world ... like the wooden sake 'masu' in Japan, which is typically served overflowing (as a gesture of bounty and courtesy to the customer) whereas normal modern glasses are only filled the usual 3/4 way. The overflowing bowl of rice or noodles is similar - and if you finish ALL of it, it can sometimes be interpreted as a subtle insult to the chef (because it means that the other dishes didn't satisfy you so you gorged instead on 'the filler'). So, rice and rice products are inexpensive in the East and so their cuisine expresses it's bounty that way ... whereas in America our bounty is typically expressed in meat dishes and (if you live on the coast) seafood.
You can also see echoes of it when comparing Italian-American cuisine to authentic Italian cuisine ... the former tends to be meat & sauce heavy (the more expensive ingredients), whereas in traditional italian there's very little meat and the sauce is more of a condiment rather than the main dish.
Getting back to American restaurants - many trendy restaurants, if they lack an edge on their competitors in food quality or special dishes, will compete instead by increasing the portion size.
