I can name a pretty good number a possible VP candidates that are superior to Pence, and tactically make sense. Why pick a guy from a state that is pretty much a runaway win for Trump. Pence also carries a significant amount of baggage. What type of voters does Pence bring with him, that haven't already pledged to support Trump? Pence isn't swaying fence-sitters, he's solidifying the base...but the base alone, won't win Trump the election. It's a honestly confusing pick.
Easy: social conservatives - from outside Indiana. He's cutting the rank-and-file legs out from underneath the #NeverTrump crybaby Elites.