In a recent post on the NVIDIA blog, GeForce Now general manager Phil Eisler said:
"As we approach a paid service, some publishers may choose to remove games before the trial period ends. Ultimately, they maintain control over their content and decide whether the game you purchase includes streaming on GeForce NOW. Meanwhile, others will bring games back as they continue to realize GeForce NOW's value (stay tuned for more on that).
As the transition period comes to completion, game removals should be few and far between, with new games added to GeForce NOW each week."
Just a few days ago, the service also lost access to Activision Blizzard's titles due to what NVIDIA calls a "misunderstanding." The developer apparently wanted a commercial agreement with NVIDIA, which is now hoping to mend the relationship and offer its games again.
NVIDIA didn't explain why Bethesda's games will no longer be part of GeForce Now. But if its absence on the platform doesn't bother you, then you can sign up for a free or a paid account, since the service came out of beta in early February. The latter option, called Founders membership, costs $5 a month for a year, though the first three months are free.