Because we have enough chickens

Sentient is a bit of a stretch for chickens.

To answer the rest of it, there are meat birds and egg layers. Meat birds grow fast and are ready to harvest in a few months. Egg layers produce more and larger eggs. We have a variety of egg layers, 9 hens and a rooster. We get between 5 and 8 eggs a day which is plenty for us.

The cost of owning chickens is a really flexible number. My wife wanted to try and loved it so we have put more money in. Our first setup was a small coop for 3 birds for around $200, the birds were cheap enough not to matter in the equation, another $100 or so in food and water things, feed, grit, calcium, etc…

She liked it so we upgraded to a $1000 coop and more birds. Not calculating the monthly payments on the coop we probably spend $20-30 a month on maintenance (feed, grit, shell, straw)

One reason those cooked rotisserie chickens are so cheap is because they are used to get people in the store to buy other things. So the store takes a hit on them but they end up making money from other stuff that may not have sold.

Also, scaling up a chicken farm, especially one focused on either eggs or meat, reduces the cost per animal by a lot. If you’re buying a single chick to raise, it’s gonna be 3 to 50 dollars depending on breed. If you’re buying 30,000 they are gonna be a hell of a lot cheaper.

I have seen mice eat each other alive. I’m 100% sure they would build a mousetrap