From what I hear they mostly subbed out Fallout 76 to other studios. That is why it was a POS IMO. They let them try some wild stuff, then when the world declared it was a big steaming pile of crap they reeled it back in by adding human NPC questgivers which is what it should have shipped with in the first place. They will probably massage it for a few more years into something reasonable, but it will never feel like Fallout 5 which is sort of what everyone wanted, not what we got.
I think its taking forever because they are making a brand new IP Starfield, doing some new stuff they have never done before, and after the fallout 76 fiasco I'm pretty damn sure they need to knock one out of the park.
I played the crap out of Oblivion, but I modded the crap out of it too, that was a ton of fun just tinkering so I can relate Game dev is like crack.
We won't let you know when it's done because we'll all be ash lol.