I'm not saying nobody should eat out, but to do it every day just seems wasteful. And I find cooking to be quite a bit more enriching than takeout.
Number 1 was social. People went out for lunch in groups, and it was an "enforced" break in the day. It's a cultural issue that can be hard to replicate for "lunch bringers" in some places. Not so fun to eat alone in a drab lunch room if your friends and peers are down the street having pizza, I guess.
Number 2 was time, or at least the perception of time. Tech people (in my context) tend to work long hours and whether you are trying to maintain a social life or bring up a couple of kids, once you add that to work hours there isn't a ton left. More than one person I know had commented that they didn't find the time to make and bring lunches that didn't leave them feeling left out. It's easy to bring a crappy sandwich, harder to bring something you really enjoy. At least for them.
This is what I liked while working in HP. We had a canteen where pretty much everybody went. You could buy a number of simple cheaper meals, a fancy expensive meal, or bring your own thing. Everybody could still sit together.
And if everyone chooses to eat cheap lunch, we could all just work less, and the system would be balanced again ;).