The Witchvox article Where Did Aleister Crowley's Influence On Wicca Go? helps to explain:
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As Gardners most well-known book Witchcraft Today came to rise, his popularity grew and lectures and classes were demanded of him. He saw a great chance for the rise of Witchcraft and the Old Religion (despite how new it was) in the modern world. It was Valiente who spoke with Gardner about her concerns that the cult would never go beyond what Crowley accomplished if the work relied so heavily on Crowleys rituals, to which Gardner responded, Well, if you think you can do any better, go ahead. That was enough for Valiente. She took up the task and rewrote the original Book of Shadows removing everything she spotted of Crowley that she deemed unnecessary and obvious (Valiente 2008, 60-61) . This was the first major change of Gardners cult, resulting in the transformation of heavy ceremonial-based rituals to that which is considered today to simulate more of an old format in reconstructionist fashion.
http://www.witchvox.com/va/dt_va.html?a=usne&c=words&id=15552
and <snip>
The Charge of the Goddess first began appearing in publications by Gerald Gardner in the late 1940's or early '50's. He claimed it was an ancient text originating in the Roman era. Shortly after Gardner's publication of The Charge, variations of it by Doreen Valiente and Alister Crowley began circulating.
http://www.awhitewitchsbookofshadows.com/Charge-Goddess.html
It seems to me that Valiente wanted to get the references and rituals away from Crowley, the O.T.O., and the G.D. as far as possible in the early years. I believe that she borrowed heavily from the writings of Lucius Apuleius in The Golden Ass for the Charge.