Contracts are a pretty gray area. In a lot of contexts, a handshake agreement or email exchange, if documented well enough, can constitute a binding, legally enforceable contract. It doesn't have to be on a paper saying OFFICIAL CONTRACT with signatures at the bottom.
Why aren't they contracts? When I sign up for a website, I have to enter into a contract for their Terms & Conditions, which usually includes the Privacy Policy.
Why do people treat them like contracts?