I have made a previous post regarding this situation, and will repeat since it seems to deserve the attention.
First, it is not likely that the people reporting a "fragrance smell" are actually having olfactory hallucinations, and the manufacturers are not lying. So, the only realistic explanation is the shipping and storage of the 20 mule team. Guess what other items are housed along side the borax, heavily chemically scented laundry products. The scent is so strong the containers need not be opened. You can go blindfolded and stumbling about the market and easily find the laundry detergent aisle by the strong scent.
20 Mule Team would need to first "bag" the contents, in addition to "boxing" so as to keep the foreign scent from entering.