Ultimately the "why" is bc the dev decided so. I do hope the infographic is clear enough, though: the blocks each have a subtle asymmetric pattern, and discerning the correct sequence of rotations relies on figuring out which side of the blocks needs to be made to point "up" at each step.

I understand what to do, but not "why"... :(

Don't know what to tell you. The logic is as shown above. It was a huge pain in the ass, but I did manage to figure it out.

I still don't see the logic in this at all. How is the player supposed to figure what this mean? And why do you have to do it twice?