It's Frontier's choice that the block feature blocks instancing (and it has only ever been strengthened and made easier to use over time), just as it was Frontier's choice to permit each player to shoot at anything they instance with.
Which includes menu exit and the block feature - as there are no limitations on their use.
Yes, of course this includes blocking and menu Exit.
What I dont understand, is that quite lot of people simply insist that blocking and whatsoever is totally fine, but deny that in open play a certain risk of being attacked by other players might be given, instead they keep on asking "why" ... because it's Open and because it's possible.