Strange Curve in Main Line

I realize there are other forums this could well apply to, as well, but I'll start here. The Main line (now SEPTA's R5/Amtrak's Harrisburg corridor) has a strange curve in it just after it leaves Philadelphia. From 30th St to Overbrook it's straight, as well as after Wynnewood. However, between those stations, it makes a large, sweeping curve to the north. Why is this?

The best explanations I've come up with are that the PRR either wanted to (a) avoid fighting over land with the Catholic Church, as the Borromeo Seminary sits right in what would be the path, if the line went straight, or (b) hit Narberth, which was a thriving community at the time. I suppose it could have also been both, or neither. Any input?

My guess is the same reason as for Horse Shoe Curve, to have a longer line to climb the same elevation as a direct line, but on an easier grade.
From the start of the curve near Woodbine Ave., the Main Line uses the valley of Mill Creek to Merion Station, instead of immediately attacking the hill between Mill and Indian Creeks. The continuation of this "S" curve through Narberth gains more altitude than just continuing to follow the creek, so that Indian Creek is crossed on a high fill. Even so, this was helper engine territory until ConRail shifted through freight to the old Reading RR.
Lancaster Pike isn't straight from Overbrook to Wynnewood, either. It has a sharp bend at the toll house near the Seminary.
The original Main Line, from the top of Belmont Inclined Plane to Ardmore, made an even greater curve, through Bala and Cynwyd, crossing Montgomery Pike 4 or 6 times in that distance.