For the first 70 years of the last century, the majority of the medical profession recommended all boys be circumcised and some even advocated mandatory universal circumcision. The depiction of the circumcised penis in medical books is just to advance that agenda and an effort to normalize the abnormal. At first, it was in the sincere belief that it was beneficial to the man's health or that men were too sexual and it benefited the man or his wife to partially sexually cripple him. Once it became ingrained in the profession, it was no longer necessary that there be any concrete benefit, only superflourous and ethereal benefits like the social justifications or the comfort (to the father) that the son would look like the father. Of course, the profit motive was also a strong influence.