Veltharis ap Rylix
Legend
I think it's just the matter of Ghosts of Saltmarsh not being branded as a Greyhawk book - it was nominally set there, sure, but essentially only by virtue of reprinting/updating older modules that assumed Greyhawk as the default setting. Frankly, the same could be said for most of the material in Tales from the Yawning Portal, despite the Yawning Portal itself being in Waterdeep.I would agree with you with one exception: Ghosts of Saltmarsh didn't open up Greyhawk.
Now granted it was an adventure compilation nominally set in Greyhawk, but I also doubt we're getting a second Spelljammer adventure or Dragonlance adventure, so I don't understand why they didn't just make it available back then. I think the fact that we know there is no "Greyhawk specific" adventure coming out in the next year just reinforces my confusion.