Lots of times the stratified seed if left until spring in a stratification box, ground or cool place will smile or grin and send out tails. Knock the tails off when planting in the spring and the seed is done for good and will not germinate.
Ginseng also does better if planted in the fall. It gets to set in the rich soil over the winter. Alternating temps such as freezing and thawing tends to be good for the seed. Seed planted in the fall correctly will have all winter to settle in and make good contact with the soil. Seed that does not make good contact with the soil will not make it.
In my early days I planted seed in the fall one time and did not walk the beds down correctly. Did my best not to step on the seed beds. Big mistake on my part. However, I did manage to accidentally step in the beds here and there when planting. The following spring seeds came up in my footsteps but no where else.
Walking the beds down over and over and over is one great key to good germination.
I am sure there are other good reasons but these are the ones that come to mind for me.
Good luck,
Latt