I think the issue is trying to cram that much into such a small space and have it process through the intestines in time for it to be useful. I think there is grazing from the time they get up to the time they go to bed, with larger amounts taken in at more traditional meal times (if they even have those).

I know on some randonnees, inexperienced organisers have presented traditional-style breakfasts, when stuff like pasta and lunch sandwiches would have been more appropriate.

The high-energy content of bars and drink mixes are an important part of the regimen, too. At least, based on my experience doing LD events.