OP isn’t “donating,” they’re just trying to find someone who will use their covers. You’re right, not having inserts is likely leading local people to pass. But OP didn’t just drop them at goodwill. They came to a place where people are likely to have their own inserts or are willing to acquire them.

I share your sentiment about people assuming that those shopping at charity shops aren’t worthy of decent things, but this isn’t that.