Why would a business throw out dog food when they can donate?

I have a friend that works at a large discount department store.(WallyWorld). My friend told me that they throw away dog food at his store. I understand if it's expired but he say's they throw it away if they accidently ripped the bag just a little. Couldn't they donate it to animal shelter instead of in the garbage? Isn't it that simple or there is more to it? Thanks :)