That's certainly part of it, but I also think part of it is due to the economics of running a restaurant. Margins are getting thinner and thinner as people don'

That's certainly part of it, but I also think part of it is due to the economics of running a restaurant. Margins are getting thinner and thinner as people don't want to pay more for the same food (despite this being how inflation works), so one strategy is to charge more and offer larger portions. The cost of a larger portion is minimal relative to the higher price (especially in dishes that are made in large batches anyways). So the restaurant is happy to be getting enough to cover all their costs (and hopefully a little extra), and the customer leaves happy despite paying more. The downsides in the long-term are that (1) as time goes on and currency inflates, portion sizes get larger and (2) people get used to larger portion sizes and the same meal has less value to the customer over time. I don't have any data to back this up, but I do believe this sort of feedback loop plays a role in obesity.