Compared to butterflies and pigs, chickens give the lowest iMG / Mood bonuses but produce the most resources.
I don't see how a grain collector would be an efficient machine when (at higher levels of AK) you could fill one in a few chickens anyway.
Now, if it collected grain and automatically bundled it into bushels, that could be an interesting mechanic. Perhaps you would have to load fuel cells into it to make that work.
Grain really isn't that useful in any great quantity (except on Pi day when my friend decide she wanted see if there was a badge for 1009 Pi's - there isn't)
Chickens are useful for the drops, so you need to do the squeezing yourself
Just because one animal collection is automated doesn't mean another should be. In fact I prefer different-ness. It's more Glitchy. Wood trees have a different mechanic to the other, and that is difference is Good Thing.
I don't know if TS will agree with me though. They took the difference- ness away from strawberry seeds and egg trees, which I am greatly disappointed with