Arguably the teams aren't combined since they have such disparate priorities/preferences. Obsidian wants to go deep and Bethesda wants to go wide and shallow, those are the kinds of games they both prefer to build. (Or at least that's how they seem from outside perspectives.) It certainly would be incredible to see some games try for more interesting compromises of "both", but it's also incredibly hard to project manage and budget and build if you are trying to go both deep and wide at the same time. Maybe Microsoft will find a way to do it at some point.
(As something of an aside/tangent, as a failed game developer I've always wished for the ability to "scout" locations in other people's games. Hollywood keeps a number of backlots of standing sets that just about anyone can rent to use. Plus real world cities can be shot by anyone looking to fill out the right permits. But games still rarely to never "share backlots" and game players and reviewers/critics still generally "punish" games that do [compare reviews of Saints Row 3 and Saints Row 4, for instance]. Imagine if movies got bad reviews every time they were set in New York. "Can you believe yet another movie set in New York? How uncreative," said no one ever. It could be incredible if as a game story writer I could "shoot" a deep story somewhere in Starfield. Sure mods exist and sort of fill that role some of the time, but mods still have that too strongly bound association with the parent game [can't sell it standalone] and monetization for mods is still complicated and players/reviewers/critics still look down on their noses for mods. "Imagine if this modder had built their own game for this story how much better it could have been?" That story might not exist to be told without "sets and costumes" to easily borrow as a foundation. I don't have any easy solutions to this conflict between wide and deep games, but I do think more access and better reviews for people trying to write deep stories in someone else's wide sandbox could be a start.)
(As something of an aside/tangent, as a failed game developer I've always wished for the ability to "scout" locations in other people's games. Hollywood keeps a number of backlots of standing sets that just about anyone can rent to use. Plus real world cities can be shot by anyone looking to fill out the right permits. But games still rarely to never "share backlots" and game players and reviewers/critics still generally "punish" games that do [compare reviews of Saints Row 3 and Saints Row 4, for instance]. Imagine if movies got bad reviews every time they were set in New York. "Can you believe yet another movie set in New York? How uncreative," said no one ever. It could be incredible if as a game story writer I could "shoot" a deep story somewhere in Starfield. Sure mods exist and sort of fill that role some of the time, but mods still have that too strongly bound association with the parent game [can't sell it standalone] and monetization for mods is still complicated and players/reviewers/critics still look down on their noses for mods. "Imagine if this modder had built their own game for this story how much better it could have been?" That story might not exist to be told without "sets and costumes" to easily borrow as a foundation. I don't have any easy solutions to this conflict between wide and deep games, but I do think more access and better reviews for people trying to write deep stories in someone else's wide sandbox could be a start.)