Maybe it's that we only pause to observe them and realize they're beautiful, when we're feeling safe enough?

"Beautiful sunset" evokes being on a calm sea shore with a loved one, feeling safe. It does not evoke being on a farm and looking up while doing chores and wishing they'd be over already. It does not evoke being stranded on an island, half-starved to death.

We think it's beautiful because it's like a background that we don't have to think about. If that background were hostile, we'd have to think and we would not think it looks beautiful.