I think it is a combination of both of those thoughts. I also think that many adults swing those hips once and let it fall. I have to remind them that they must continue to swing those hips - one time just won't do the trick.

Yes, but WHY do adults only swing those hips once? Is it because it feels somehow dirty? Is it because they just don't understand how hoops work? Why do kids inherently know to keep swinging, and grown ups dont?

Just as with any type of learning- children are more able to learn things quickly just by watching and imitating what they see over and over again (this is called Conditioning). You know the saying 'you can't teach an old dog new tricks', well that is true to a certain extent. Adults can't learn a language as quickly as a 5 or 6 year old can. Children instictually imitate, adults are stuck in thier ways. An adult might look at the hoop and say "this is kids stuff, I can't do that", while a child will pick it up and say "wow, this is so cool, I can do it". And from the mouths of babes we all learn about the power of positive speech. Besides, if a larger and heavier hoop is easier for an adult to move, imagine how much easier it is for a child to move it.

As a 52 Y.O., I'd just like to say that my reluctance at first was partly due to the "lacivious" appearance hooping lends itself to. I am SO over that! I also believe that as we grow older we sometimes need to be reminded how to REALLY move again.
peace y'all!