I think the biggest threat to the generic lines is the fact that they have to compete against other generic stuff that's produced cheaper. So they need to differentiate. Amazon is filled to the brim with the no-name generic building blocks that are not as high quality as Lego, and apparently you can't differentiate purely base don the quality alone.
Even in clothing, there are less and less, not high-fashion but high quality for not totally unreasonable price brands.