My bet is the straight party vote helps the democrats in voter fraud. It is much easier to mark a ballot once for straight democrat when stuffing ballot boxes with ballots than to have to mark each and every name. The same is true when paying the homeless to vote (if they have to look for each name, they may screw it up).
I think you are right.....it's easier to use mail-in absantee ballots for vote-fraud straight-tickets.....