The Elder Scrolls 5: Skyrim never received a spin-off similar to Fallout: New Vegas due to the presence of The Elder Scrolls Online, according to former Skyrim co-lead designer Kurt Kuhlmann.
Kuhlmann, a 20-year veteran of the studio, told FRVR (via VGC) that The Elder Scrolls Online served to keep fans of the series engaged, thereby allowing Bethesda to focus on other projects. "I do think The Elder Scrolls Online took the heat off," Kuhlmann stated. "There was a new Elder Scrolls product, and it was ongoing. It was creating new content constantly."
He explained that while The Elder Scrolls had historically been a single-player franchise, The Elder Scrolls Online became the primary Elder Scrolls experience for many players. "There are a lot of people… I mean, I know [there are] the single-player people, I'm one of those people - but there are a lot of people to whom The Elder Scrolls is now The Elder Scrolls Online. That's their experience with it. That's what they love."
Another contributing factor, Kuhlmann suggested, was the critical acclaim of Fallout: New Vegas, which fostered a perception of rivalry between Bethesda and New Vegas developer Obsidian. "The whole New Vegas thing did create this - at least the perception of this - 'Who makes a better Fallout game? Oh, they should just give it to Obsidian' [situation]," he noted. "There are the Obsidian, New Vegas people that think obviously New Vegas is way better, Obsidian is way better at making those games, and why don't they just get Fallout altogether."
According to Kuhlmann, series director Todd Howard aimed to avoid a similar dynamic within The Elder Scrolls series. "Todd, from my time there, he is very protective of it," Kuhlmann added.
Obsidian has recently been confirmed to be working on a new Fallout game in collaboration with Bethesda, following significant layoffs across the Xbox division. Obsidian has since been moved under Bethesda's purview. Meanwhile, The Elder Scrolls Online studio Zenimax Online has undergone severe cuts, leading to a revised scope for future content, though the studio has reiterated that ESO will continue.
The Elder Scrolls 6 remains in development, with Bethesda asserting that the recent layoffs have not impacted its development roadmap. The game currently has no announced release target.