I think there's also liability issues, like if they give away food and someone gets salmonella poisoning or has an allergic reaction or something then they could get sued. It sucks but it's not completely arbitrary.

That's a myth. Good Samaritan laws exempt that

In addition to possible bad press, it’s also common for people to not know the law. And as I read news stories asking if the reader knew the difference between “best before”, “sell by”, and “use by”, I would also expect some to destroy the produce out of a misguided but kind desire to avoid harming those who they could legally and effectively help.

Doesn't get rid of bad press.

Throwing away food is a common practice also in production factories to keep prices fixed. If a resource supply becomes too much available compared to its demand, the price lowers, and we aren't anymore at the "get an apple from a tree and sell it" level: if the price lowers too much entire production or distribution companies can go bankrupt.

It stinks badly, but is a sad reality.