Sometimes it seems like these things are synchronized (we know Cemetery Dance will announce (re-announce, really, since some editions have already been sold) their The Stand at some point in the next x months, and I think multiple Carries and Salem's Lots appeared not far from each other not too long ago, although I may well be off on the dates).
I'm not saying it actually is, or that we should blame any of them, it's just...odd.
Or maybe not so odd, given that King's first 6 or so titles hold real drawing power for collectors and the temptation (or need, really) to farm the fertile ground is inescapable.