Y head symbolism stems from Pan the Greek god's influence which had a resurgence in England in the mid 1800s. Thats my theory. Pans character is somewhat malleable as a god, but extreme lust, representing wild nature, and a lack of traditional morals as a consequence of living in the wild and being a half man half goat. Pan's influence in the occult can be seen through the devil getting cloven hooves and horns from him, Aleister Crowleys obsession with Pan, and Baphomet being a creative construct strongly derived from him. The Y symbol cult, desiring absolute freedom without morals and the freedom to act like beasts would be drawn very heavily to the concept of Pan or worshiping Pan as a god.
forgot to complete my extended sentence "but extreme lust….etc…are constants."