This is important. If they won't eat it, they're not getting the lauded nutrients. Below a relevant quote from Robinson that I posted on another thread:
I think you are right to trust your birds' instincts.
no-one is suggesting that a single grain is a complete feed. What you seemed to be missing in your earlier post is that grains (plural, variety of) are the main constituent in purchased so-called complete chicken feed. I see that now you state it (para 5), so maybe it's just a misunderstanding.