IMO this may be for 2 reasons:
1. Microsoft is their new publisher
2. what Obsidian said in the game title description. Direct cut and paste from Grounded's Steam page:
To paraphrase: We've insightfully learned from our experiences (and mistakes) in developing our game titles in the past. This most likely included a front seat ticket witnessing Bugthesda's ongoing dumpster fire that is F76. Finally given that M$ is our new official publisher, we now have the potential to expand our PC based franchises to the highly profitable console gamer market. So it would be prudent business sense to build in an innate multi player capability of the game in alpha phase. So the fan base, YTer influencers and professional industry critics the likes of IGN etc. alike will have tons of time to audit, excoriate, champion or shame online features of said multiplayer mode. But unlike Bugthesda, we're not going to divorce and abandon our core PC gaming fan base for the micro transaction infested, multi billion dollar, glitzy Golden Goose that is the console gaming market.
Or something like that.
Anyways, if they maintain this level of transparency that other alpha titles (the likes of EGS and SubNautica) have to date, then this strategy will definitely benefit them financially in the long run when the game releases. Especially since they're NOT taking hundred of millions in backer funding. Like a certain game that-will-not-be-mentioned-here which has been in alpha phase/Early Release for the past 7+ years. And which now appears to be shifting 100% of its dev focus to
producing the perfect road map to reboot the game's now abandoned road map....
Source: https://www.youtube.com/watch?v=vpyYxqEe--o&feature=emb_logo
You simply. CANNOT. Make. Any. Of. This. Up.
Thank God for industry devs like Obsidian and CDProjekt Red. At least they've produced actual GOTY single player games. Regardless of what production schedule slips or setbacks they've experienced during game development, they've always managed to release their past games within the finite human lifetime of their fan bases.