Ive seen it practised with almost 360 degree turn, and understand your point about uke's role as in should they just keep holding, but if done correctly there is no mistaking ukes role, they will remain transfixed through their own forward momentum, constantly off balance, trying to stand upright and guided around by nage ??
Why doesn't uke just let go? You might find contemplation of that question rewarding. "Because that's the kata" is not the correct answer. Rather, uke holds on because the connection protects him. But where's the attack? If you don't know, you probably aren't doing this exercise correctly.
FWIW, I didn't find the video Janet posted particularly convincing. It looks to me -- especially in the third segment -- like uke could stand upright and recover her balance quite easily. Think about why, and what nage might do to fix the problem.