Kurt Kuhlmann, former lead designer of Skyrim with 20 years of experience at Bethesda, told FRVR that The Elder Scrolls Online "relieved the tension" around the series.
There was a new Elder Scrolls product, and it continued to evolve. New content was constantly being created for it.
According to Kuhlmann, for many players, ESO is now The Elder Scrolls:
There are people who like single-player games, I am one of them, but for many, The Elder Scrolls is now The Elder Scrolls Online. This is their experience and this is what they probably want more of.
Another reason he believes is the success of Fallout: New Vegas, which led to the opinion that Obsidian handles Fallout better than Bethesda.
The whole New Vegas story created, at least this perception, a situation: "Who makes the best Fallout? Just give the series to Obsidian."
Kuhlmann believes that Todd Howard did not want a repeat of such a situation with The Elder Scrolls:
He is very protective of this series.
Now Obsidian is indeed working on a new Fallout together with Bethesda, and The Elder Scrolls VI remains in development with no announced release date.