Seriously? It's because they bought into the "free love" movements and new-age "I'm spiritual, not religious" thinking. They've had sex with too many different men, can't recall them all, and feel life is meaningless. Literally, much of their life has been drained out of them, so then run from one cause to another and jump on any new-age fad of the week looking for something to fill the void in their souls.
I have a cousin like that, wholly given over to the dark side. She's more than 10 years younger than me but looks 20 years older, and I'm a grandma!!