Answer: Because West Virginia had more density of organic materials back in that time.
Step-by-step explanation:
This is because gas and oil is produced by the decomposition of organic materials.
As virginia was covered with swamps, under the actual surface we can find a lot of organic material (the remains of the swamps and such) while in Winsconsin, under the surface there are mostly rock, so there is not a lot of organic material that can be descomposed to produce oil or gas.