Because films’ promotions may deliberately conceal information about tragic events in the story to achieve maximum impact and nobody thinks that is unethical.
This feels a lot like talking to Eliza. Your replies very vaguely connect to what’s being discussed in this thread, but there’s just no substance or coherency to the argument.
"When a film makes you sad you are aware of what's going on" is your claim, but I don't see how that applies to something like, say, Terminator 2, whose entire goal, according to Cameron, was "making the audience cry for the Terminator," yet was not promoted as a sad film. It's hard to come up with a principled difference here.