Why do vertical artworks have so much impact?

The answer is quite simple:

We are used to seeing artwork displayed horizontally on a wall.  Therefore, and automatically, a vertically-oriented artwork will be more unique, and if done correctly, it can make an immense impact to the space since it spawns a bigger surprise.

Why are vertical artworks less common?

My opinion, from an artist standpoint, is that it's a vicious circle.  There's a higher demand for a more traditionally-oriented horizontal artwork, and so artists produce more of it to meet demand.  When creating artwork, artists fall into the trap of horizontal perspective since that is more sought after.  When it comes to landscape and nature photography, cameras were made in a horizontal orientation, so it's little wonder why we have a plethora of horizontal images.  Less vertical artworks and images are produced.  There are fewer vertical artworks made, more horizontal artworks are displayed, and the vicious circle continues.

So what do you say we break this vicious cycle?

If the wall space is right, consider vertical impact.