It hasn't been expressly said or stated, but there might have been an accidental deadline coinciding with the company being purchased by Microsoft.
I'm not 100% certain of the legality of buying a game studio (Obsidian) who is already slated to launch a title (Outer Worlds) that has commitments to retailers but I imagine that part of the agreement was for the game to release as planned before Microsoft would assume full and direct control. This is evidenced to me by the fact that
A) The game released on all systems and was not an XBOX exclusive.
B) Take Two (old publisher) was able to make an exclusivity deal with Epic Game Store, something that Microsoft doesn't typically do (they would go on to launch all Halo games on Steam)
With that said, I imagine that Microsoft likely pushed for Obsidian to "hurry up and finish" thier current project very quickly so they could start on the next project, which would likely be a Microsoft Exclusive. For me, it looks that way because.
A) Outer Worlds feels rushed as fuck in many places, some places comically so.
B) Outer Worlds didn't have a release date (October 25th) until June 9th of the same year. Four months is a very small window between "Announcing Release Date" and "Actual Release Date".
C) It also didn't have a full year between it's annoucement date (Dec, 201

and it's release date (Oct, 2019) which is another very small window.
It feels very likely that pre-Microsoft that Outer Worlds wouldn't have a October 25th, 2019 release date, or any release date, until much later. Microsoft purchased Obsidian in November, 2018 (possibly earlier) but probably couldn't do anything about thier existing obligations (with Take Two, Sony, and later Epic) and all they were likely able to do was to push the release out as hard/fast as they were able to do. Microsoft bought them to make First-Party, XBOX exclusive games and they'd likely like them earlier than 2023.