Flow occurs only because of pressure. No pressure, no flow. A glass of water has lots of flow potential, but no pressure, so it just sits there.
If you pressurize the galley, the resultant pressure causes the oil to flow into all the passages and cracks we want it to go to. If you pressurize it from both ends, it still will go into those areas but the pressure is better supported and presumably more even across the galley.
This concept is very common and popular in EFI fuel systems. A good system running 45-60PSI won't have the last injector hanging out at the end of the line....it is plumbed in a loop so that there is no end of line injector.
We want oil flow in the oil passages that feed off the galley. The galley serves as a manifold, or distribution block, if you will. The flow in the galley is only a byproduct of the fact that when oil exits the passages, it has to be replaced by more oil. A big galley feeding smaller sized passages is what we want - and it's what we have, more or less. The better supported the pressure is in the galley, the better we can assure good oil flow down the passages. A double-end fed galley will have a better supported pressure, all else being equal.