I can't speak for others, but I have a pretty limited tolerance for very explicit, heavy depictions of violence, for bad things happening to animals, or for downer endings.
I fully recognize that these don't make for bad cinema. I also recognize that they're often more effective as surprises. But they are going to dramatically cut into how much I enjoy a movie. And movies aren't like books, where if the tone isn't quite what you're in the mood for you just stop reading, they're more immediately confrontational, and backing out is a bigger deal (and almost a faux pas, walking out of a movie is seen as commentary on its quality). Previews are also going to avoid spoiling twists or dramatic moments, which, again, makes sense, but makes them poor tools for assessing tone. This means I'm often tempted to read the plot summary before watching, which feels silly, but if I want to challenge myself and watch things not quite to my taste and things that aren't just kid's movies without just sometimes paying for the pleasure of having a bad time, I'm not sure how else to approach it.
It also feels like other people have almost the opposite perspective, where of a movie doesn't have something really emotionally heavy or challenging to watch they can't take it seriously. I'm not sure what makes sense here, and maybe my tastes are just the problem, but it feels bad to spend fifteen dollars and two hours of my time to be in a space that's too loud, has only very expensive food, and leave depressed by what feels to be to be an overly cynical or myopic message or an artistic vision obsessively depicting the many ways human beings can be physically harmed, in as much detail as possible. Again, I don't think it's bad or wrong, I certainly don't want it to be banned or require disclosure, I just struggle to decide where I fit in the market, and I worry that my purchasing patterns support a narrative that leads to less of what I want.