IIRC, it's cheaper from a mass-production standpoint. Less time needs to be spent on balancing the rotating assembly and less material needs to be added to balance it. Instead, it's just done from either end of the crank with larger bob weights.
If I understand this and can explain it, Ford reduced the overall weight of the 5.0 crankshaft, to save money or something.
With the traditional 28 oz crank, there was enough room to put all the mass needed to balance the crank into the cast counterweights, except for the 28 oz part. That part went on the damper and flexplate.
With the lighter crank, they reduced the amount of material on the crank, and it required the added weight on the balancer and flexplate.
Apparently when you go to the stroker, since everything gets farther away from the crank centerline, it is easier to use the crank that is less unbalanced to start with.
If someone can explain this in more detail with the math, it would be good also.