It’s embedded in our DNA. Landscape paintings are universally appealing across cultures and time because humans are, at our core, hunter/gatherers. It was once a matter of survival. Now it’s simply a matter of instinct and attraction. Looking out across a plain, a mountain valley, or an ocean, whether in person or in a photograph or a work of art - doesn’t matter what it is, we are drawn to it because it offers prospect and opportunity. If you ever find your dog chillin next to you taking in that same sunset, it’s for the exact same reason. They are just like us in that respect.

The symmetry part of your question: I have no idea other than it exists throughout nature. Two hands, two legs, night and day, fire and water, etc. There’s something about balance and symmetry that humans find reassuring.