Obsidian Entertainment was adding Steam achievements to The Outer Worlds hours prior to making the move to Epic
Some information that the developers weren't aware of the exclusive as the steam database indicated steam achievements were being added to the steam store a few hours before the announcement. If the developers were aware they would have waited another year to put achievements for a game that wouldn't be available for Steam until 1 year later.
We also reported last February that a release date of August 6 was added to the game’s Steam DB before being removed shortly after. With The Outer Worlds coming to Steam only next year and the fact that Epic Store doesn’t support achievements, there is not really a reason for the devs to add achievements the Steam DB this early.