I've planted all over BC. Seed trees started being a thing early nineties and they don't do it everywhere. Quite often its because there aren't species needed as seed trees that won't already grow back are already slated for nursery production and replanting.

Smaller block sizes act this way too, the boundaries are seeded from the older growth on the perimeter.

Deciduous trees like poplar, Adler, and birch are like weeds and will grow very quickly and compete for a time with replanted trees. Eventually the evergreens tend to choke them out by taking over the canopy and changing the soil with their needles.