I do think there's a cultural thing involved. Here in the UK just now long hair is fashionable (I suspect it started with Jennifer Anniston), which is great, but it's still very rare to see a Causasian woman with hair much longer than waist-length. In fact I could probably count the number of times I've seen such a sight in my whole life on my fingers. By far the majority of women you see here with really long hair are Indian / Pakistani / Bengali, of which we have sizeable communities.

But it's not just fashion. There's a genetic factor involved too. How long hair will grow is dependant on speed of growth and the life-span of the individual hair. At least among European women, it's only a very small, lucky minority who can grow their hair below their bums, however much they try. People like Leona are very unusual.