It's moreso about the general trend that's happening where everything must be sanitized and advertiser-friendly. Like, is it really that far-fetched for an action thriller movie, that contains guns and people using them, to also have a gun on the poster? Do we really need to protect society from that?
Plus, movie posters are art to a number of people. Someone very specifically chose the lighting, the expression, pose, and background to convey a message about the movie. But now it's being censored because "gun scary."
I, for one, don't welcome the bland, homogenized world that corporations are trying to turn everything into.