Steefel wrote about this traditionalist / modernist duplicity in his book Duchamp’s Glass in the Development of His Art:

The individual talent draws from tradition the strength to go ahead and, by being of the present, revivifies and transforms the past.
[…] his whole approach is intimately involved with problems of perspective and disorder, and with perspective on himself, in the widest sense of the word “perspective”. Hence Duchamp’s irony and his seriousness, his absurdity and his logic, in life and art.

Steefel, 1977, page 8-10

He also says that Duchamp aims at a four dimensional point outside the work. I believe that is only accessible to the observer through the written notes because these texts are not only about the fourth dimension, they also show the vanishing point of this imaginary fourth dimensional perspective system of the Large Glass.
The reason why these boxes are successful and crucial for the recent art history is the randomness associated to their interpretation and the conceptual structure they created for a masterpiece (the Large Glass – Fig. 5) that would be probably ignored without them. Duchamp plays a game with ironic, serious, irrational, scientific, humorous and dramatic references. These become a catalyst for a sequence of events in the observer’s mind.

All in all the creative act is not performed by the artist alone; the spectator brings the work in contact with the external world by deciphering and interpreting its inner qualifications and thus adds his contribution to the creative act.

Duchamp, as quoted by Steefel, 1977, page390