Earlier quoted context omitted.
Doesn't AWS also have the same problem? Someone could upload encrypted illegal content, then later law enforcement could discover the key. Why hasn't AWS gotten in trouble for that yet?
No large cloud provider allows anonymous usage. They take down content on request and assist law enforcement in catching the non-anonymous people doing illegal things on their platforms.
Also, I'm not sure what scenario in which you would be able to find the encryption key, yet not have access to the wallet controlling the contracts? Even if you did, I'm not sure why hosts could not assist in cancelling contracts in a similar fashion to cloud providers taking down content on request.