They were running short on ways to settle ties. Though once you start focusing on the second-half record, why worry about making it intraleague? You might as well just look at the whole record for the last 81 games. Also, if two teams finish with the same record and the same intradivision record, the implication is that the team with the worse interleague record wins, since to get the better intraleague record, they'd have to have the worse interleague record.