Because in this era of half-baked, bug-filled, and horrible game releases, the current "beta" of Bannerlord is (now) quite decent.
Unfortunately, the game is still far from what I had expected from TaleWorlds after all these years, but I don't think the majority of the game's playerbase has even played Warband (or even followed the development). They don't care about the canceled features. They care about the game as it is right now, and compared to all the other crappy releases out there, and oh boy was Bannerlord a crappy release too, the current version is enjoyable. And that's probably why the reviews are positive.
Hopefully, I'll be able to change my negative review of the game in the future.