I notice that except for small commuter bikes and older bikes (before the 80s), hardly any of the larger and/or sportier bikes have covers to protect their chains: ![Honda Cub](https://i.stack.imgur.com/atzBP.jpg). ![Hero Honda Passion](https://i.stack.imgur.com/aGGuP.jpg)

They seem quite practical, and conducive to chain life- by protecting the chain from the elements and requiring less frequent lubrication. Then why don't larger bikes have them? Is it purely for aesthetic reasons? Or is there a safety aspect as well? Are there other reasons? What would happen if the chain broke in a bike with a chain cover?