The issue for MS is, Sony and Nintendo don't want Game Pass on their platforms at all, in its current form, and I can't blame them. What deal do they get from MS from getting a cut off Game Pass subscriptions through their platforms, versus 30% cuts off B2P game sales of those same titles on their platforms, where the former is better financially for them?
I just don't see where it happens, unless Microsoft makes significant changes to how they structure Game Pass on those platforms. And at that point, Sony & Nintendo would probably want Microsoft to implement those same changes for Game Pass on Xbox platforms, too. Because why have a loophole exist where Xbox consoles get the games Day 1 on Game Pass, but Sony & Nintendo don't want Day 1 for those games on their services or Game Pass custom to their platforms due to cutting into B2P sales revenue?
Elden Ring had the benefit of being on PS4 & PS5 platforms which contributed heavily to overall sales. Starfield does not have that benefit. Previous Bethesda games like Fallout 4 and Skyrim got to the numbers they did in large part due to PlayStation (and in Skyrim's case, also Nintendo) platforms.
Without a PlayStation release, Starfield isn't getting beyond 15 million lifetime sales. That's lifetime, as in 4-5 years, so it'll sell slower than Elden Ring did. They need PlayStation & Nintendo if they hope to get beyond 14-15 million lifetime sales for Starfield.