Why a bicycle frame has hollow pipes other than solid metal bars?

A bicycle frame is typically made of hollow pipes rather than solid metal bars for several reasons. Firstly, hollow pipes provide a good balance between strength and weight, making the bicycle lighter and easier to handle. Secondly, the hollow design allows for internal cable routing, which protects the cables from dirt and debris, improving the bike's performance and longevity. Additionally, the hollow structure of the pipes can also help absorb vibrations and shocks from the road, providing a smoother and more comfortable ride for the cyclist.