

because it feels off balance.
the level of the horizon is a key part of composition. it effects comfort, balance, and groundedness. when the horizon is not level it will feel disorienting, dizzy, or chaotic. yes, you can break compositional rules for artistic effect, but you need to learn the rules and why they matter before you can do so effectively. the example you posted below doesn’t really make your case. it’s not that great of a photo, rotated or not. to intentionally rotate the horizon to give it an uncomfortable or disorienting feeling is fine if that’s the goal hell, maybe it’s more to feel otherworldly or any other number of things you can derive from it. the point is that you need a reason and intent behind the unlevel horizon. what feeling were you trying to invoke by not having the ground beneath the feet of the viewer?
i mean this is all very dependent on time, place, and people. there are people that were fully nomadic at all times of human history. they certainly didn’t stay in a town either. some people did travel, clearly. devout religious folk, merchants, well to do young men… there have always been exceptions, but on the whole as a norm, over 500 years ago most people didn’t travel much. and more to my point, pilgrims traveling like that likely didn’t have maps most of the time. they likely got directions to the next town by the people that lived there.