Some people genuinely are exposed to enough darkness irl that they don’t find enjoyment anymore in stories featuring nuances of misery, gore, and trauma. That’s totally fine.
Nope, it's just explaining there's a demand for non-grimdark work that Compelling Science Fiction's audience can compose of. There's no protection involved. Magazines select works to sell altogether as a product. If CSF's brand is non-grimdark, hard scifi, and they are successful at selling the product that is non-grimdark, hard scifi, then there's an audience interested in buying their work.
I'm not really sure where you get the protecting clause from, or intent. It's just market forces.