Answer: It's because they like me.
Where I work, we have an on-site cafeteria. The level of tastiness of the offerings is unpredictable, but having the option on site sure is convenient, since we don't have anything nearby that we can walk to. And there are some consistent items, like the salad bar and deli sandwiches, that one can eat in a pinch.
So, what you probably don't know about me is that I'm sickeningly nice almost all the time. In any given transaction, I probably say "please" and "thank you" about a dozen times. Once, when I called a friend at her family's house, her brother who answered the phone gave me crap about being too polite. "Fuck you!" I replied. Fictitiously.
Anyway, I am very polite to service workers, and when I see them on a regular basis, I try to find out their names and have just enough small talk to make the interactions friendly without slowing them down in their jobs. (Aside: This is different from my mother. Woe betide the supermarket cashier who asks her how she is.) In a nutshell, I treat the staff of the work cafeteria the way I would treat my coworker acquaintances, because . . . they are coworker acquaintances. Apparently, this attitude is unusual in my office.
As a result, the staff tend to like me and they sometimes do favors for me. Like, the cashier sometimes doesn't charge me the quarter for my daily giant cup of water. The chef tells me when he's going to make my favorite soup. The sandwich maker automatically puts dijon mustard on my veggie wrap. And the guy in charge of serving the "healthy choice" entrees piles ten times more food into my container than he puts in anyone else's.
I've tried to explain to him (politely!) that for me, more isn't better in this area. Especially since the healthy choice entrees I am likely to try are typically some form of pasta with veggies or tomato sauce. But he always just smiles and keeps putting more in, sometimes brushing me off with an "it's good for you." I've finally stopped begging him to stop after every giant spoonful, even though it's really horribly wasteful to have to get rid of three-quarters of the meal. (Why don't I share with someone or save the leftovers for the next day? It's never really that good.)
Today, I weighed my orecchiette with roma tomatoes, basil, fat-free mozzarella, and garlic (which still ended up pretty much tasteless) on the salad bar scale: 1.34 pounds. Of pasta, basically, since there was but one tomato in my container. So, more than a full standard package of pasta. That's what people want you to eat if you're nice.