Why does it seem like the trends from decades past recycle every 30 years or so?

Now, I have only lived in 4 decades, but in that short time I have seen the same basic trends come and go. Bell bottoms became flared bottoms. Bootie shorts became daisy duke’s. Platform shoes come and go, neon and off the shoulder shirts are coming back in. Long hair on guys is fashionable again and the punk look has always been the same. Feathered hair, shoulder pads, skinny jeans…

Are we just out of ideas? Is there really nothing new out there? For those of you who have lived in a few more decades than I, has it been this way since you can remember, or is this a more contemporary thing?