Hormones. A broody hen's natural instinct is to defend her nest.Well, I took the eggs yesterday, when she was briefly off the nest, taking some food. She didn't see me do it. I swapped the 11 real eggs for 4 wooden imitation eggs. She's sitting on them now.
I tried giving her some live food last night -- a favorite! -- and she attacked me. She pecked so hard that I thought she'd broken the skin on my hand. That's unusual for a bird that is normally so good-natured. So I guess she's not too happy about the change in her eggs.
Not sure what happens next.
I strongly suggest breaking her or at least removing the wooden nest eggs and hoping she abandons the nest. Generally, fake eggs are utilized to encourage brooding behavior. Since these obviously don't hatch, she may not give up on the nest which would increase the likelihood of her wasting away or at the very least, puts additional unnecessary strain on her health.
There is no point in keeping her perpetually broody if you are not wanting her to raise any offspring. Check out his article for reference.
https://backyardpoultry.iamcountryside.com/chickens-101/when-breaking-a-broody-hen-is-necessary/