I think Bethesda is building up a base of fans with the more generic settings of TES that are populated with the easily identifiable Humans until they can make a game with Morrowind's strangeness again.
TES 6. Introduce our Magnum Opis. Set the game in an entirely unique setting to capitalize on our new fan base and capture the minds of a generation of gamers. Lots of interesting unique lore and quests.
As true as this may be, which I'm sure this is how the Dev's are doing things, I just have a gut feeling that the graphics part has a lot to do with the fan base. Look at Final Fantasy. Yeah they started out in the old "over the head view" style in NES, but with each new game the graphics seemed to improve more and more. I would always hear people talking about how awesome FF games looked in comparison to other popular games with lesser graphical beauty, and honestly I was right there with them (just never got into FF games cause of the turn-based style).
But I think that if Morrowind had been a project that was held off until now, or at least until the year TES IV was released, I'm sure the fan base for TES would skyrocket. I had SO much fun with Morrowind but xbox ruined it for me with it's constant crashing (Microsoft just couldn't handle the epicness of The Elder Scrolls III). All I'm saying is that though lore has a major role in fan base I'm sure things would turn out better in their favor if they'd bring back the odd-ness of Morrowind back.