The biggest factor is the $3000 price point.
I think the biggest factor is making a VR headset that is comfortable and practical to use for hours on end for
mundane purposes (if they're going for "serious" uses).
Stereoscopic 3D is potentially headache-inducing because it doesn't match up with your head movements, eye movements and focus. Maybe goggles can do better on those fronts, but if they're a bit off, or a bit laggy the disorientation and stress will be back. If your goggles let you walk on the moon, battle zombie hoards or spend a few minutes walking through a building plan then you might put up with a bit of discomfort - but if you have to spend the day in meetings, do you really want to spend it getting a headache while dressing up as a member of Daft Punk, talking through your office wall to colleagues who's computer-generated faces (they're wearing goggles IRL so you'll be talking to an emoticon) are making eye-contact with an image of you, groping for your cup of meatspace coffee...?
What
actual advantages does it bring over looking at a screen?
It
could be really good -
if it is 100% convincing, if the AR integrates seamlessly with your real surroundings, if its so good for so many things that you wear the goggles all day without noticing - but a bad dose of "uncanny valley" could result in this being a massive flop. It's also going to need some
genius user interface design to make people want to use it all day, and I haven't seen much of that around in the last few years (maybe all the UI geniuses are busy working on AR?).
The danger is that if Apple have sunk a load of cash into this, there may be pressure to push it out before it is ready, which could discredit the idea.
I'm thinking particularly of the Newton which largely flopped because it got a high-profile launch before it was really ready. I don't think Plan A was "OK, this may flop, but in 10 years time, after we've nearly gone bust and effectively been taken over by NeXT, we'll release a world-beating mobile phone, and the ARM processor that we helped develop for it will rule the world and eventually run the Mac... sorry, what, we had to sell our ARM shares to pay the electric bill? Dang!".... and even though the Newton's big downfall - handwriting recognition - works pretty well these days, nobody seems to be using it much...