Rashi says that the reason why you put the bread of an eiruv chazerot in a house is because you are joining up all the houses together but I don't understand why by an eiruv chazerot you are joining up the houses together but you are joining up the Chatzeiros together to make them all 1 reshus so that you can carry inside them from your house so if so you shouldn't put the bread in one of the houses you should out it in the Chatzer like you do by a Shutaf Mavo'os.
Benzi, London
Since Eruvei Chatzeros joins the houses together so that one can both take out to and in from the Chazer and also carry from one house to another, we have to join the houses together by putting everyone's Eruv in a house. If we were just joining the Chatzeros we would indeed put in one Chazer, but as Eruv Chatzeros allows taking from one house to another (which wouldn't be permitted otherwise) it requires that it be placed in a house, since otherwise one could carry only within the Chatzeros from one to another but not into another house, since it is a private place and a different Reshus.
Yoel Domb
But rashi says over here that the reason y u need an eiruv chazerot is in order to carry from my house to the chatzer not in order to carry from my house to your house and also since over here we r speaking about a communal chatzer and a flat of houses so wat issur is there for me to carry from my house to ur house the whole issur is because by travelling to ur house I am going through a chatzer which is a separate reshus but over here both of our houses are in the same block of flats so I'm not going to a separate reshus because I'm not even going through the chatzer to get to your house