Zenimax Media = Parent Company, makes money and manages it so we can have all of these great games
Bethesda Softworks = Publishing company, pretty much the decision maker for how the games get made
Then Zenimax studios and Bethesda Studios. Companies two primary developers.
They still own their stuff, and the original creators of this who reside within Bethesda Softworks and Zenimax Media can do with their game what they want. They made the proper decision to separate the companies for this MMO project as not to delay an complicate what Bethesda Studios does best. TES is not dead and never will be as long as gaming exists.
Yea and there are also a bunch of other studios like id software and arkane studios.