They don't mean it. They don't even understand it.
The original pagan religions were real, substantive religions that prescribed codes of conduct, held certain behavior to be virtuous and other behavior to be evil. They functioned as the moral and ethical guides for their respective societes.
This New Age stuff doesn't really focus on those aspects of pagan religion. The new age Norse religion seems to be a cover for white supremacists. Modern Wiccans are a bunch of middle-aged hippie chicks who like to go naked in the woods, and the men who want to bed them.
The old religions are dead- trying to revive them in a society like ours makes no sense. The original religions, like any religion, grew organically to serve the needs of their respective societies. You can't just transplant a religion over centuries into a completely different culture and society.
Lewis was well read in the Classics (his day job) and the Edda and Sagas. He commented elsewhere that it would be worth reviving Paganism just to see a gaggle of cabinet ministers trying to sacrifice a white bull!
Nobody who has read the Edda (elder or younger) has any illusions about Norse paganism. The problem is that nobody is reading them any more!