That doesn't show a lot being already done, it's just a tiny sample of things they were working on. It's using like one town out of 60 lol. None of that necessarily worked smoothly, just enough that it could be used in short clips. They had to balance and bugfix all sorts of things they're obviously not going to show in a promo vid. Making a trailer that looks like it could be from a complete game is both easy and common for game companies. Be glad they didn't sell the game based on hyping a trailer but worked on making a game that isn't released as a broken mess like Fallout 76 or No Man's Sky.
People have understandable complaints about certain issues the game has, but I can still play the sandbox or campain for hundreds of hours with no major bugs, and relatively few minor ones. I have no performance issues on a less than amazing PC on fairly high settings, as well. The info in game is largely accurate, the controls reasonably smooth, the troops reasonably responsive to commands, etc. etc. All kinds of things you might not think about that aren't represented visually in something like a trailer, but that you'd certainly notice while playing.
So yeah, people know. The game was developed, it took awhile because they're a relatively small developer and it was a fairly ambitious project, since Bannerlord/Mount and Blade generally has a lot of little moving parts, interacting systems, that more simplistic gameplay doesn't.
Anyone thinking this game is some sort of disaster or scandal is deluded or has very little experience with the gaming industry.