The 11 and 13 aren't far apart, but between 60th Street in SW Philly and 6th Street in Darby, they are on opposite sides of CSX, which is a relatively impermeable barrier, so they serve different markets. For passengers, the importance of the connections at Darby TC to the 113, 114, and 115 have only gone up, as job sprawl continues to be an issue. Also, consolidating the terminals of the 11 and 13 allows SEPTA to have more flexibility during disruptions to either line, and also lets SEPTA downgrade the amount it spends on upkeep of crew rest facilities at Yeadon Loop, which is currently a very necessary, and nontrivial, expense.