Well, that's an easy answer. Fermented feed is not designed for optimal growth it's designed for optimal health.
A simple example of this is simple volume/weight ratios. Let's say you have 2lbs of dry chicken feed split across two chickens, so each chicken gets 1lb of feed.
One lb of feed is our dry baseline, so it has a ratio of 100% nutrition/1 part weight/1 part volume. Each chicken can consume infinite nutrition but only limited amounts of volume, and to some degree, limited weight. So the dry feed has a ratio of 100%/1/1, and that's about what the chicken will eat in a day. They can only eat 1 part volume before they stop eating.
Then there's the 1lb of feed you ferment. It's nutritional content/absorption/etc and micro nutrients like antioxidants and good bacteria have increased to give a total increase of 10% additional nutrition. But it's volume has increased by double and it's weight has quadrupled. So the nutrition/volume/weight ratios go from 100/1/1 to 110/2/4.
So when you feed it out, the chicken on the dry feed consumes 1lb of dry feed, It gets 100 parts nutrition to it's one part volume. The chicken on the fermented feed gets 55 parts nutrition for the one part volume. But for the same amount of feed, you can feed the same chicken for two days instead of one. Chickens on FF tend to grow slower and eat less. They take longer to grow out and don't eat as much as quickly.
If your metric for success is fast growing big chickens, fermented feed is a bit of a flop. CAFO operations will raise a chicken in 6-8 weeks. Fermented operations are more likely to finish at 10-12 weeks. But if your metric for success is an inexpensive healthy bird, a chicken that feels the need to eat constantly will be healthier on FF because it will eat less and absorb more nutrition per lb of dry food. Your pen will smell better because the poop will have less nutrition in it to rot. Your birds will have robust, healthy digestive systems. The reduced weight leads to more activity. There's less waste of feed overall because they get more out of it. The FCR tends to be comparable despite the longer growth period.
So it's really more about what do you value. Incidentally, some brands of commercial chicken feed actually DO include fermented soybean, corn or alfalfa meal in their feed, just dried and pelleted. And large scale operations DO use these feeds. But they are less effective than live bacteria and they do not produce much healthier birds.
Most fairs only care about weight to age ratio, and that the birds can walk and are clean enough to not look awful. Health isn't a strong metric considered, whether it's in fairs or the commercial industry. And that actually creates a shuttle of people going from being kids interested in agriculture, going straight into the CAFO production system instead of exploring other more natural or otherwise healthier options. The only thing that is promoted as success in agriculture is bigger, faster animals. Healthy, robust, sustainable animals are not a metric of success in conventional agriculture and they don't make as much money.
