It's better to scrap 5 years of investment than over a decade of goodwill towards a franchise.
Uhm... It's Bethesda Gane Studios' good will that has been built up over a decade. And they are not involved with TESO beyond serving as consultants on lore.
Zenimax Online Studios is the subsidiary of Zenimax Media, the owners of Bethesda and all that came with them, including the Elder Scrolls IP, that is developing this game. ZOS was founded expressly for the purpose of online game development. And what better IP to use than Elder Scrolls to launch a major MMO with? Especially since they own the IP.
So the goodwill from Bethesda you speak of in not being scrapped. You'll see The Elder Scrolls VI in about three years. Same as you would if TESO was never announced. That's about how long it takes them to get a TES sequel completed and released.
What Zenimax Media does with the IPs it owns is not up to the developers. TESO started development five years ago. Zenimax Media could have directed Bethesda to develop it instead of Skyrim. But they didn't. They formed a new team and staffed it up independently of Bethesda for the purpose if this and any other future online games the company wants to pursue. Skyrim's development went undisturbed, as did TESO's development. Bethesda Game Studios has a budger and so does Zenimax Online Studios. And I would say a lot more went into developing Skyrim than previous TES titles. So that suggests to me that the budget increased.
So you don't like MMOs? Nobody says you have to play TESO when it comes out. But I love MMOs. I love TES. So I will at least give it a try.