hiding blocklists is not only technically impossible, since it can be reverse-engineered via smurfs like you say, from outside, in the free world...
...it's philosophically kind of Orwellian:
Not only do they not want content from the blocked instance, they don't want their users to know what and from where they are missing. It's gaslighting their own users into ignorance, and attempting to not only block the content, but block the fact that these other places exist.
It's very disrespectful to their own users, treating them like they don't deserve to be able to make up their own minds, so they should not be allowed to inform themselves if they want. It's an attempt at a kind of mental enslavement.
But because the attempt is also technically impossible, it's just an iron fist of impotence.