Wicca's relatively new as an official religion (out of the World Broom Closet by Gardner in the 1950's) so there could very well be a generation who grew up with it, but it's not one of the major world religions (yet) and I keep hearing stories about Wiccan parents either being rejected by their children, or wanting to remain private with their faith instead of making it part of family life because...well, personal issues, perfectly within individual rights, but it just saddens me to see an opportunity to represent just go like that.
Other times, it's a friend who saw it on TV, did the research the TV/movie thing was based on, it suits them, it might suit their friends and they want to see...
Other times, it's aspects. Like, I wanted to practice Buddhism after watching a movie I forgot the title of "7 years in tibet" or something, just because I liked how kind they were to animals. I was kind of animals, but I was considered eccentric. Buddhism seemed like an opportunity to validate my "eccentricity"...and then I did more research into the lineages and such and it was just, nah, not entirely for me. But that's what got me looking it up, that there was a teeny tiny bit of a wound there from the society I lived in that would think respect for life could get too weird.
So, I'm definitely overgeneralizing if I say that the same draw to Wicca could be disempowerment, especially by patriarchal culture--which even modern Westerners have, not as obviously, but still has many of those undercurrents much as we'd all like to go, "Yay, we're all past that. Gender-egalitarianism for everybody." Someone hears "the Goddess" and it fulfills a personal need (that's been clouded and dismissed by society) for some hint of feminine divinity. Or it could be environmentalism, the harmony with the natural environment. It could be the witchcraft aspect of Wicca. It could be the fertility aspect, even. It could be that they've met Wiccans, not even grown close enough yet to be friends, and they just seem like really nice and serene people! And their faith is a large part of their life, so, somebody new to that could get interested.
"They" will have as many reasons as there are individuals within that "they", for feeling called to the Wiccan path.