These are often run by script kiddies on machines which they have cracked. The reason for such a location is that an IRC bot is not always used simply to maintain control over a channel (a task which is handled for the operator now on virtually every network except EFnet).
Indeed, some "war bots" exist solely to aid in takeovers of IRC channels that do not belong to the user. Since even script kiddies are smart enough not to run such a program on their own system, they often crack the systems of other for that express purpose.