Most trailers don’t show the actual game? Or have nothing to do with how the game will actually be?
I’m sorry, but that’s pretty misleading. There are lots of game developers and publishers (perhaps even most) that simply show clips of the game and what actually happens in it like they always did. For example, every recent trailer Nintendo’s posted has pretty much entirely featured content from the game itself.
The trailer for Breath of the Wild is pretty much entirely game footage. The endless Pokemon Sun and Moon trailers are game footage. The trailers for Paper Mario Color Splash were about 95% in game footage and 5% characters commenting on in game footage. And something like this is pretty much 100% true to the game:
A lot of games still come with traditional gameplay trailers, and gamers really appreciate that.