I suspect that some image makers are more comfortable making high-key images, while others tend towards low-key. Image viewers may have similar preferences.
Some words that I associate with each:
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High key: joyful, active, optimistic, pretty, airy, growth, …
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Low key: calm, passive, pessimistic, reflective, peril, threatening, ugly, honesty, truthful, death, …
These also depend on subject matter, of course. Similar associations come with high or low saturation, and where the points of interest lie within the image, and so on.
If a photographer tends towards low-key images and wants to break away from that, I suggest exercises that start by considering paintings. Rembrandt or Cezanne? Munch or Manet? Which resonate most, and why?
Then take photos that are deliberately high key. Frame the image so only a small proportion of the image is in shadow. Imagine a gray card in the scene, and ensure that most of the scene is lighter than the gray card. Then edit the images accordingly.