I agree with you, but my one point would be that we know we're returning to two classic settings this year, but that doesn't inherently mean campaign setting books. I'm personally hoping if we get a Spelljammer book, it's an adventure - I personally have no idea how to run a Spelljammer game, and would find that way more useful than a setting book.
And we know that there's one classic setting that will only get a cameo. Nothing but the Krynn UA has nailed down which settings those are yet. Spelljammer could still be the cameo with the races presented in a Guide to the Multiverse style book. Or as player options in a multiverse module.
Same reason as anyone else. Escapist fantasy.
Like a goofy fun April fools joke that hurts no one.
In fairness, Spelljammer and Planescape both kind of lend themselves to cameo appearances.
Except the fans who desperately want to see the return of a favorite setting.
There are Birthright fans right now* who would weep tears of joy just to have WotC remember to make fun of their setting. It would prove they even remember its existence.
In qddition, we have the moderator confirmed leakwr from Reddit, who months ago called Radiant Citadel and Dragonlance in addition to Spelljammer.
