So you believe the apostles resorted to Oujia boards, rather than revelation, after Jesus left them? Interesting.
A lottery device was used to usher Mathias in, sorry but that is the way it happened. Reason why, to rule out human subjectivity and make sure the decision was divinely approved, hence "chance" to us, but controlled by God (Was their thinking). Each Apostle had there "man" and consensus was not reached. Well, they casted lots, not used their own will.