HoMM4, as I've said, has changed the world. Old world was destroyed because there was quite a few story errors or incosistences (sp?) so they wanted to started anew. HoMM4 vanilla campaign has the best campaigns from HoMM games to date, yet there was not much known about the world. Nival could easily expand on that - set the story into yet unknown parts of the Axeoth (that was its name, wasn't it?) and even make some references to known events, like Emilia's or Lysander's kingdom, something about pirates connected to Tawni Balfour, or whatever they fancied. Instead of that we got a generic fantasy world with we-are-not-Christian Haven, let's-burn-and-destroy-everything Inferno, BDSM Dark Elves, HoMM3-copypasta Wizards, etc. Also: Gryffin eternal!!!111!!ELEVEN!
HoMM 4 was a world change. And so was HoMM V. HoMM V changed it to the world used in all of the subsequent Ubisoft-published M&M games - Dark Messiah, HoMM V + Expansions, Clash of Heroes & MMH VI (I think it's used in that one). But no, Ubisoft decided to create their own world for all of their own-made games, and I don't see a problem with that. It gives them the flexibility to use different studios and to create games of different kinds without affecting the lore of the previous games. Heck, The Settlers changed once Ubisoft had acquired Blue Byte (2001+, so The Settlers 5 onwards). It's gone from a historical series to something a bit more fantastical. The Settlers 5 was a bit of a wobbly moment, but The Settlers 6 and 7 have been quite good, albeit very different games (TS6 is more akin to a RTS than a game of economics, trade and so on). Each one is in a different place, too. TS7 is in the all-new Tandria, and it's also where the iOS game The Settlers of Tandria is set, and I *think* it's also where The Settlers Online takes place.
Yep. Change to as generic world as it can get. And with elements of other games too - Nival's creative department probably had holidays when they were making HoMM 5.