I'm not sure why he picked Pence but it's possible he wants the more conservative Republicans to be with him. Trump has touted about being not really part of the "establishment" but now he has Pence who is a cookie cutter version of the GOP uber conservative establishment. Trump may have scared off some moderates but otherwise he may have been looking for someone who seems level headed and like an average guy. Pence is in no way an average guy though. He's a nut job who will try to take away everyone's rights but Trump wanted to do that anyway. He may get some of Indiana's vote but Pence isn't actually very popular in Indiana. More people dislike him than like him. I'm not sure why Trump would pick someone who is already not very well liked in his own home state.