"Fallout: New Vegas" is an alternative work in the Fallout series, and it is also the only Fallout game made by Obsidian Entertainment, but for Obsidian Entertainment, Bethesda still has a lot of IP that can be mined, just like the "old rolling" The Elder Scrolls. The former Obsidian Entertainment co-founder said they had also wanted to make an Elder Scrolls game, but Bethesda didn't agree.
Whether it's Fallout or The Elder Scrolls Online, it often takes years to make a new title, and former Obsidian Entertainment co-founder Chris **Ellone once proposed to Bethesda to make a new Elder Scrolls game, just as Fallout: New Vegas was somewhere between Fallout 3 and Fallout 4, providing more adventure during Bethesda's development gap. At the same time, it will allow Obsidian Entertainment and Bethesda to establish a similar partnership between Treyarch and Activision. However, until Chris **Ellone left Obsidian Entertainment, these plans were rejected by Bethesda. Because Bethesda wasn't too happy with the response to Fallout: New Vegas.
Todd Howard, the head of Bethesda Game Studios, has also hesitated to outsource Fallout 5. But now that Obsidian and Bethesda have become a family, there may really be a wonderful chemistry between two game studios with a lot of experience in RPGs.