The scuttlebutt is (at least from one guy and his super-leet insider sources) that Jo Ann Emerson didn't want her district to take in too much territory in the St. Louis media market.
That's surprising seeing as how she lives in St. Louis with her husband who's a Democratic union member.
..and some of the district is a part of the St. Louis media market (St. Francois, Washington and Iron counties), and Ste. Genevieve County is as well.
As for Jefferson County, why don't they just carve it into two districts: have the cities/suburban Jefferson County moved into one of the St. Louis districts (pretty much everything from Crystal City north to Arnold) and then everything south of Crystal City (rural/podunk parts of the county) into MO-08? Seems like that would be less controversial.