I don't think Microsoft has a lot of confidence Starfield will be a system-seller. Otherwise, as you said, we'd be seeing Starfield/Series X bundles, and themed Series S & X Starfield consoles.
I kinda wonder what the morale is over at Bethesda; from the document leaks and even couple of interviews it feels like Pete Hines is not particularly enthused with the Zenimax/Microsoft arrangement. Shinji Mikami promptly left shortly after Hi-Fi Rush despite not retiring. Some of the same workplace culture issues that existed pre-acquisition are still there in post (not a good sign for ABK), etc.
Now imagine having worked on this massive WRPG for like a decade and having envisioned it for longer, less than a month out from release and...virtually nothing noteworthy in terms of marketing. No demos to whet the appetites before launch, no further information outside of the June Starfield Direct (which didn't give a full feel for the actual gameplay loop). The whole mood around the game corporate-wise seems oddly mute and maybe that is a sign the game's coming in hot.
Even so, I have to imagine more than a few people at Bethesda who've put years into the game are not pleased with this seemingly ho-hum rollout for what's been billed as Bethesda'a most ambitious game ever made :/