Actually it's not true that folklorists have been using morphological analysis for a hundred years. The practice was discredited several decades ago, partly on account of unreliabilty and partly because it was impossible to rule out bias on the part of the analyist. As one pundit put it, "it's amazing to see how many so called 'objective analyses lead the reader right back to the analyst's country of origin".

But mostly the method ran out of steam simply because of its lack of utility. To put it another way, people don't tell folktales or sing folksongs because the tales or songs originated in Asia or Europe or anywhere else. They tell folktales and sing folksongs because they find something in the tale or song which makes it worth singing or saying.