For Republicans, each state has some variant of a have a winner-take-all system of awarding delegates to the party convention, while democrats rack up delegates according to the percentage of votes they get. Those methods generally fit with the parties' personalities, says John Green of the University of Akron.
GREEN: The democrats really value representation perhaps because they’re so diverse so they have this emphasis on proportionality. The republicans value other things. They value consensus. They like to bring the party together even if it’s done by the rules rather than voters.
Green says that’s because the Republicans have a long history of being a minority party. Like most other states, Ohio is winner take all for the Republicans, but proportional for the Democrats.