Lack of compactness
In our current system, the people of Evansville are represented by the same congressman as the people of Warren County, west of Purdue University. What do these people have in common? Nothing - except being good Hoosiers.
Warren County is closer to Milwaukee than it is to the southern part of the 8th district.
The people of Monticello are represented by the same person as those in Bedford. Do those communities have the same interests?
NEXT: Lack of competition