In the fact that phallic worship has, for so many generations, been looked upon as something to be hidden; in the fact that it received ecclesiastical condemnation where there was no downright denial of its existence; in the taboo so continuously and ecumenically imposed upon its expression; and in the feeling that any discussion concerning it was tantamount to an admission of bawdy tastes; no doubt lie the main reasons for the neglect which the subject has received by writers and historians generally.
Source: wiktionary