Why contemporary art is so difficult to understand?

This question started from the concept of 'canvas'. 

After WW2, artists started to be sceptical about human rationality. And the canvas was the symbol of human's rationality in art area. So artists stop drawing real world and started to figure about the real way to think what is the real meaning of canvas- which is related with human rationality and history of art. Is the canvas is the real world? Does a canvas truly show what artist wants to express? 

So artists started to do experiment with canvas. They started to minimise their technique on canvas so that they can express their concerns unlike before. So that is why modern art and contemporary art- which is called 'just one line on an empty canvas' started to begin.