Because the correct term, of course, is jerry-built. 
Both are correct, according to my old 12-pound dictionary.
Jury-rigged is something temporarily built on a ship.
Jerry-built is temporarily made from cheap materials. It is derived from jury-rigged. During WW I and WW II, the “Jerry” part took on an angle of an ethnic insult to Germans.
You are correct, sir.
My comment was designed to point out that some, perhaps most, people use the incorrect term jerry-rigged when they mean either jury rigged or jerry built.
I was being too obligue it seems.
Jeez, and I have always believed that both versions of the term were derivatives of the French, du jour, meaning “for the day,” or temporary.
and now I wonder. xo, C.