There's a lot to that one someone's writing about elsewhere.
Once the Hollywood facade falls away, what are you left with? You're left with a very vast school of knowledge, most of the time without a teacher.
I don't know if it's just the American culture, but anything you have to work for is too hard, so people don't generally persue it. That's pretty much anything. That's why you have a vast majority of people without higher education (we're going to hop around on Wikipedia for some of these points I'm making).
But I digress, let's look at the 'Wicca' situation.
First off, let's call a spade a dirty 'ole shovel. Let's call it Witchcraft. Why? Because it's derived from a lot of things, which to the amateur student, is a lot of information to partake of.
Let's look at history. Let your jaw drop, because there is a LOT of history involved. The creation of the magickal system can be accredited to a lot of sources, including Kabbalah, a mysticism of judaic origins. Throw in a large collection of eastern mysticism (and yes, every one of those links has corresponding elements in the rituals and beliefs of witchcraft). But...that is even before you get to the history of some of the men and women who introduced it to the public and you've got a whole other area of history to work on. Then, if you'd like to get technical and do some research on how Wicca became recognized as a religion in america, then you've got more modern history (like the issues with pentacles being allowed on gravestones, which is a big step in becoming a more common, more 'acceptable' religion during modern times).
Overwhelmed yet? We're not even started.
Herbs is another big fascination. Why? Because witches are concerned about their enviroment and the natural order of things, so herbal remedies are something that they would look towards instead of modern medicines (and if you're lucky, on the internet someone will sell you something to help you out....gotta love capitalism). But if you're going to study that, well, you might as well know some of the magical uses of them. Only the Gods know if if it's really going to make a difference, but it doesn't hurt, does it? So many different places with so many different meanings, but with the idea of hermetic princples and the law of correspondence, well it can't do anything but help.
Divination is another area of study. Runes are getting more popular, but you have Futhark and it's variations, a greek oracle of runes, the MODERN divination tool called druid sticks, and then your older tried and true forms like geomancy and Tarot (Yeah, I forgot the name of what a friend of mine was researching, but it had to do with stones, their proper types, their alignments to the planets, and the 'casting' of them for purpose). And that's if you're not straining your eyeballs scrying.
History. Herbs. Divination. I would say that those are the big ones that most people wind up moving into. Not many really research the nature of the path, the anthropology of it, nor do they really want to think of it as a science (refer to hermetic princples) and get an understanding of how the universe works, or themselves for that matter. It is far easier for someone to dictate to them HOW something works, as opposed to WHY it works. Most 'students' of witchcraft want to be spoonfed and have everything available to study at their leisure.
That's not how it works, kids.
Gather information. Check, double-check, triple-check, and if something new and exciting comes along, cross-reference it to something else you found somewhere else that kind of makes sense. Keep learing. Keep gathering information. Power comes from knowledge, but the ultimate goal is understanding. I believe that is the true Craft of a Witch.
My two cents.