Because it's a videogame and that's part of the process. I dunno, I made a long post about it a few days ago, but the whole you lie thing is what's embarrassing - hell, I'm just too close to the process I suppose since I've been doing it for so long, but code is sent to agencies who cut trailers with such lead times that development sometimes changes before master. Especially in late q&a cycles. This isn't new or anything, people see not intentionally setting out to lie to anyone haha. Maybe things need to change a bit since Theres so much vitriol these days, but its being gone about the wrong way: threads like this and the WD ones are the very reason features get cut more and more. It gives the impression that all consumers care about are graphics and all reviws score on are look and feel, so scopes get diminished and features scroped to dedicate more resources to graphics and fluff elements and renderings. Sad really. Shallowification of design because publishers are afraid you're saying you won't buy a game unless it looks better than anything released previously (at the scale needed for profitability).
That's why publishers support live streams now from retail copies... So you see the master code and features and gameplay once its available, and aide your purchasing decision. No ones hiding... But nope, you get #youlie campaigns from the hard core and people shit bricks and since marketing did what they could with the content provided by devs, devs sometimes have to pay the price