With Indiana it is a tradition that goes back to a rural era in which most people were farmers and could appear at the polling place by horse-and-buggy. Closing the polling place at 8 PM ensured that people could get back home by night. Now it makes voting difficult for people whose work hours and voting times coincide. Republican pols have found that convenient.Were Indiana to lengthen polling times to 8 PM local time (as Michigan does) would give Republicans less of an advantage, and Indiana would probably vote more like Michigan. Indiana would be a swing state in close elections.
I'm really skeptical that poll closing times (and all other voting suppress tactics) are what causes Indiana to be more conservative than its neighbors.