Probably security, too: cookie data is security-critical, since you can use it for session hijacking, etc. The version doesn't leak anything about the cookie's

Probably security, too: cookie data is security-critical, since you can use it for session hijacking, etc. The version doesn't leak anything about the cookie's contents so it can be directly accessed without any security checks. The whole point of isolating the process running each website from other browser resources (like cookies) is an added layer of security.