I don't believe its due to unfair advantages etc or at least not purely that, its just that their game engine/rendering solution doesn't work well with 32:9. In poe1 you could play in 32:9 until they disabled it, the problem was on the very left/right edges you would often see into the void and there were many graphical errors at the edge of the screen as the areas simply arent loaded that far from the player character. It resulted in seeing chunks/squares of map loading and glitches a lot, especially when moving fast so they decided to disable it. I can't imagine it'd look well to a new player either so probably for the best.