Network Rail want rid of them as its a link with the past when the railway was a proper joined up railway not like now.
Alternatively, rather than it being some grand conspiracy, Network Rail are following the practice of railways on the continent and moving towards having a smaller number of signalling centres rather than a large number of smaller signal boxes. It is, of course, also worth remembering that BR closed far more signal boxes than Railtrack or Network Rail have so far managed.
