Because they like something (oats in this case) and for enrichment is a good reason.. at not more than 10% of the total daily intake.. beyond a formulated ration. It's a treat.
Nutrient profile is a bad (or rather, uninformed according to research) reason to give oats.
Oats have diminished nutrients (as does cracked corn) to a formulated ration which should make up 90% of the diet.. and is already *often* corn based,
I do not include free range access stuff as treats or diet.. but rather what is out of my control nutritionally and usually otherwise beneficial to the flock mentality.
I'm not sure what your actual ratios are.. you would wanna describe it better. I'm also not sure I have the answers either..
But The following link
from a known and trusted resource shows appropriate nutrient levels depending on age and purpose.. notice fat is pretty low across the board when compared to fat content of BOSS..
https://www.metzerfarms.com/nutritional-requirements.html
I'm not familiar with ricketts beyond possibly it being caused by poor nutrition.. IE wrong feed. Maybe influenced by internal parasite load, personal genetics, absorption issues, etc. Despite being one of the better options, I'm also not sure exactly how complete the poultry cell is or if it has what you're specifically looking for.
Through my many flock adventures, including hatching, and attention to detail disorder..
Even when ALL conditions are met for the flock some individuals will not be getting everything the need to be at well I'll say peak performance.. but really even just healthy, unfortunately.