Whats the point of informing your soldiers during a war that they are no longer belong to this army !
That's a little hyperbolic.
It is common for clubs to tell players towards the end of a season or contract that they will need to find new clubs. It's part of the game and the players know this.
It gives the agent time to find the right deal for his client and it helps the club to organise their summer window. City can't sign new players if the existing players can't be moved on.