@cprevite—as others have said, they’re very warm. My way of explaining this is that a coat of fabric X will be less warm than a cloak of the same fabric. Why? The cocoon effect. There’s a lot of warm air with you in there, which you just can’t get with a coat, and it cuts the wind magnificently. Now, no cloak I have is good enough for an Iowa winter (though maybe all six together would be), but cloak over coat will do amazingly.
As for the original question… Based on the above information, they should come back in fashion, though I doubt that they ever will, other than more poncho-like things that women can wear to fancy events. However, at my college, we have ‘Cloak Brigade’, which just means that there are a lot of us who wear cloaks around campus, so there will, on the other hand, always be people wearing them around on a regular basis—anyone who wears one becomes a member, though they may not end up hearing about it… And I certainly wear mine around town during the winter, and people comment positively on it, so maybe there’s a little bit of hope there.