Most ordinary Americans don't have eggs and bacon for breakfast any more, unless they're physical laborers who burn a lot of calories during the day. In the last couple of decades the 'traditional' American/Canadian breakfast, has become mostly a weekend, holiday, or restaurant breakfast, just like the 'full English/Scottish breakfast' as far as I know. But people do usually have cereal with milk or yogurt for a little protein, and if you add fruit and/or toast to that, and coffee, and possibly have some yogurt or a granola bar in your office in case you start to fade halfway through the morning, it usually holds you together until lunchtime. As others have said, a lot of it is just what you get used to.
It does seem to be a German custom that people expect not only a hot lunch, but to have someone else cook it for them. The whole thing about all large German offices having subsidized employee cafeterias with a full hot menu is rather unusual too from our point of view. Most US workers either bring their lunch and eat it at their desk, go out to eat a quick lunch at a casual restaurant, or pick up something to bring back to the office. (Not necessarily fast food like hamburgers or hot dogs, more often soup, a sandwich, a hearty salad with grilled chicken, a light pasta dish or pasta salad, etc.)
That said, there is something to be said for eating more earlier in the day than later. My blood sugar and energy level (what Germans might think of as Kreislauf, as a euphemism for general well-being) do better when I eat more protein earlier in the day, so I sometimes try to have some cheese or cold meat for breakfast, and I don't eat just salad for lunch.
But again, there's no reason you can't have a filling cold lunch, not just a good sandwich (with lettuce and tomato and whole-wheat bread, of course) but fruit, cheese, nuts, salad, etc. And no reason not to have a modest, not too heavy hot meal at supper, rather than a full-scale meat-and-potatoes blowout like traditional Sunday lunch at your grandmother's house.