Your wrong.
"Under the DMsGuild program, you can publish D&D material that has no setting or uses the Forgotten Realms, Ravenloft, Eberron, Ravnica, Theros, Arcavios(Strixhaven), Radiant Citadel, Spelljammer, or Dragonlance settings."
I remembered seeing Spelljammer on that list, so I double checked and it's there. The big surprise for me was so was Radiant Citadel, which had previously been treated as generic D&D instead of a seperate setting and not listed. So it rescently got promoted, perhaps to clear up confusion, perhaps because part of it showed by in the Golden Keys book, partly because they have future plans for it or a mix of all the above.
I look forward to see Witchlight: Domains of Delight Hopefully get the same treatment in the future.