This seems not to be due to curvature but due to color distribution of lines. I wonder if effect would still be visible if all lines had same color distribution.
It's not supposed to be "due to curvature". It's blindness to curvature, due to the colours.
But it is somewhat dishonest. You could color the lines in the same color as the background and then you would have "illusion" of dissapearing lines, right?
That’s not an illusion. You’d be seeing it accurately.