Why are Freenet files stored encrypted despite the key being part of the address?

The Freenet anti-censorship network identifies static files with Content Hash Keys, which consist of three parts: a hash of the encrypted version of the file, the symmetric encryption key, and some cryptographic settings. You might wonder what the point of the encryption is if the decryption key is part of the file's identifier.

Well, the only piece of information needed to single out a file is its hash, and that's all that servers store. (Besides the actual encrypted data, of course.) That fact provides a good deal of protection for server operators. Because the servers don't store and optimally never see the decryption key, the operators can't know what their servers are storing, and therefore almost certainly won't get into any trouble for it.

It also means that server operators can't read the data on their servers without a link, so they don't get anything special in regard to access by hosting.