What makes economists lump bridges, arthritis drugs, and songs together?

Question

why is the competitive market unable to achieve efficient results with these?

Answer 1

The answer to your first question is that all these things cost money to make and have some means of determining payback.

As for your second question, I dispute your premise. A competitive market can achieve efficient results with bridges, arthritis drugs and songs. Bridge contracts can be determined with competitive bidding, drugs are certainly subject to competition and songs are sold by several retailers, which is slowly driving costs lower. Do you have examples to support your premise?