The problem is that the people who make up the inner workings of all political parties are dominated by fringe and special interest groups. They're the ones primarily motivated to get involved to that degree.
Those of us who form the moderate centre are simply to busy working for a living or, unfortunately, simply unmotivated to get heavily involved.
As a result we tend to vote for the least offensive party or the one that lies the best to us and pretends to have our interest at heart. Sometimes we even get tossed a bone.