I think it just depends on a lot of different things. As someone else said, they share tracks with the spur so if they are up against time as-is they may not be able to. Also, if they are bunched up, as I have seen a bit of recently, there could be one already heading down into Walnut Locust to turn around, so they could be trying to make way.

For what its worth I've seen more than a few occasions where the local operator will make an announcement and the two trains will hold for a quick transfer. I've usually seen it at Race-Vine or Spring Garden, though. And again, it's not something that's scheduled it's more so if the two just happen to be aligned to make it happen by coincidence.