I think Bethesda in particular is getting so big that it wants a piece of the user data game, or at least manipulating their customers to give them really accurate feedback.
I could see fallout76/eso6 as the right experiment for this. They know both IP's and how they perform in the market, they have huge established fan bases. I think Fallout 76 is a lucrative diversion that will create nostalgia later on, driving future game sales and promoting that brand. I think Fallout would make a good multiplayer experience, and this particular fallout isn't fallout 6 either... The name choice is important!
If Fallout76 doesn't do well they can always recover their losses by making a single player "official fallout 6" game. If it succeeds, they can still make the single player game as well, once people are burned out of the competitive online play, a win win for everyone.
It's been a joke since an easter egg in Fallout 2 claimed the next Fallout game would be multiplayer. Back then they would have been describing multiplayer is the same sense Bauldurs Gate (and I don't mean the console spin-off) was multiplayer. So still very much a single player game, but bring your friends to combat more or less. It is worth saying that when it comes to singleplayer narratives... Well, Bethesda is not known for strong story writing in its quest lines. In fact, it's a point of contention that the quest writers often contradict the rich lore laid down by their world writers. Basically what I'm saying is it would not be hard for main storyline quest in Fallout 76 to be on par with previous games.
On the other hand, it's my opinion the monster models we've seen are incredibly lazy... And we know 76 is not from the same studio responsible for Fallout 3 and 4 (You are absolutely right its core game to the series). So I guess the strength of the singleplayer narrative in the game is up in the air. As I said before though, as long as it's even mediocre and as long as you can filter your server participation to just your friends (or even nobody), people will be happy.