It would be extremely expensive for a company to develop many activities at the same time. For instance, cosmetics, parfums and sunglasses are very specific fields on their own. Accordingly, it is easier and more affordable for a fashion company to license their trademark for use in parfums, makeup lines, sunglasses and any other are they have the desire to branch out but do not have the expertise. And it is even more frequent that fashion companies license their trademarks for core products with the outsource of manufacturing.
I have written, together with a couple of work colleagues, the licensing chapter for Brazil for the publication Getting the Deal Through Licensing 2013, which details licensing in Brazil. You can read and download it here.