Trends grow out of people's needs and activities
Trend is a word with a lot of associations: usually it is tagged with a label of transience, and trends are often viewed as negative and shallow phenomena. On the other hand, the world is full of political, economic and ecological trends with very protracted life cycles indeed.
Design trends are often technology-driven - the ancient Egyptians, for instance, used a lot of blue fabrics and paints because they had learned the required technology for manufacturing this colour. Over millennia, trends have been produced in line with the same logic: when something can be made, it will be made.
Necessary things generate demand. Fashionable clothes or trendy fabrics are not manufactured in order to be stored in warehouses or admired on store shelves - they are made for people. Trends are a part of human identity and interaction. You could say that there isn't any thing or phenomenon in which the influence of trends is not visible - everything contains a tiny trend.