Indeed, that is your opinion. Which is why when Atlus shows stuff, you can simply chose to not watch trailers if you wish to go in relatively blind.
On the other hand, I'd much rather know more about the game. I'm not a child that gets excitement out of merely holding the latest installment anymore. The mystery of trying out something new is pretty much gone for me, and if anything can end up frustrating me if I go into a game expecting that and it doesn't deliver. I get hooked on details, information. I want to know how it plays, the scope of the game, the specific mechanics. How it'll compare mechanically to previous MegaTen games. I don't need endgame spoilers or surprises laid out, but I do like to have an idea of what I'm putting my money and time into.
Persona 5, of course, has a special position given our history with the franchise, but for many other games this kind of marketing is how I end up buying them at a fraction of their original price in a steam sale or bargain bin a year or two later.