In the late 1940s there was an upsurge in organizing Pagan religions. Do you know why?

Question

You are both right, but not completely. Communications began in the late stages of WWII with people who had been under the radar for centuries. Men and women came home from the war determined to get the witchcraft laws rescinded. Gardiner wrote "High Magic's Aid" (1949) but did not mention Wicca. Later (53) he used "WICA" in "Witchcraft Today."
When the witchcraft laws died, closets opened in England and immediately began to move westward. The religion aspect of the crafts became organized.

(This is super compressed. Doreen Valiente, Russell, Clutterbuck, King and many others could have many pages.)

Answer 1

It can't be the repeal of the witchcraft laws in England -- that took place in 1951, and allowed Gerald Gardner to "go public" with what eventually became Wicca.

Good question, this one. I honestly don't know.

Answer 2

Because of a man named "Gerald Gardner" who is credited with resurrecting the religion.