Because everybody else is doing it!
Facepalm.
Anyway, in my novel which has an earlier end to the Civil War, Indiana first becomes interesting in 1876. George Custer is having a drink in Indianapolis when he throws a punch at a Republican soldier, initiating what becomes known in most circles as the Battle of Indiana.
The situation in Indiana becomes heated, General Hancock is ordered to bring forces to Indiana while Democratic Vice Presidential Candidate Thomas Hendricks calls the Indiana Rebels to disperse. Hancock resigns his position after a mysterious meeting with Colonel Levi Clarke.
Indiana is quickly pacified as the rebels report to Maryland, organize under Hancock's command, and prepare to battle against the Federal forces under General Sherman. The battle is eventually diffused as Hayes, Clarke, and Tilden decide compromise with a recount in select states.
The final count comes to Tilden - 172, Hayes - 182, Cooper - 15. Florida and South Carolina both went to Tilden, Louisiana stayed Hayes, Mississippi turned to Hayes, and Indiana, fearing that Hayes would've taken the state with the "diaspora," Indianan Democrats united with Greenbacks to give Cooper 15 votes.
Election is thrown to the House. House votes Tilden into the Presidency and Wheeler to the Vice Presidency. Judge Blaine uses his pawn Charles Guiteau to attempt to assassinate President Elect Tilden (and elevate Republican William Wheeler), only killing Erin Clarke as a result.
Indiana continues to be a battleground state. Votes for Hancock in 1880.