Manga is read backwards because that's the traditional way it's been formatted in Japanese culture. The layout and reading direction are part of the unique style.
The reason manga is read backwards is related to the way Japanese language and writing systems are structured. Also, it's been a convention in the manga industry for a long time. So, that's just how it's done.
It's mainly because of the traditional reading direction in Japanese culture. In Japan, they read from right to left, which is why manga follow that pattern.
It could be because they heard it's a unique way to notice details they might have missed otherwise. Also, for some, it's just a fun challenge or a way to break the monotony of regular reading.