I agree with the suspicions of the OP. Adding cereal crumbs during the packaging process would be a great way to get rid of waste and extend the amount of packages created. Any factory manager would see this opportunity.
Plus, who doesn’t like a little cheerio dust in their cereal?
Keeping the crumbs in there adds to the weight, hence less premium flakes they have to include.
Cost effective.
Sprinkle it on ice cream!
You give Froot Loops to animals? :eek:
Well, they’re not fit for humans, are they? 
The cereal tailings are just an ingredient in the feed formula, a small percentage. The tailings don’t really add much protein or nutrition, just, carbs, starch and sugar.
Cheerios were by far the most common because they are one of the most popular cereals.
We were adding them to pelleted fish feed for salmon and trout hatcheries. If we had quality issues forming the pellets a % boost in the cereal tailings really helped bind it together. Think about that if you are experiencing extrusion issues of your own. 
The total amount allowed was controlled by minimums and maximums within the feed formulation program, known as Brill. These parameters were set by the nutritionist.
Consider that your experiment was performed using flakes from which loose or semi-loose crumbs had already been dislodged.
Spam reported.