It doesn't even remotely resemble any of the previous games in the series.
Why do they bother calling it a Thief game?
It looks awful, but that's not the point. Deadly Shadows wasn't very good, but at least it WAS a Thief game. The setting, characters, story, and art style were very Thief. Even if that game was awful (and it wasn't), it still bore the Thief name accurately.
Why call this new one a Thief game?
It isn't brand awareness. Nobody who liked the old Thief games wants to play this game. It's not a popular, recognizable brand.
Here's my theory: They're just bad people. They take delight in seeing old franchises that were great be ruined in the most insulting way possible. They're sadists who want to cross a line.