Software often gets used for something besides its intended purpose. Someone writes a simple library to solve a simple problem. Efficiency is not an issue since

Software often gets used for something besides its intended purpose. Someone writes a simple library to solve a simple problem. Efficiency is not an issue since the problem is simple and the library is rarely used. The code is slow but it works so no one cares. But because the code actually works, the library gets shared with other programmers. Eventually someone uses it for something that has a lot of data and is run frequently. Now the inefficient code becomes a real problem. Multiply that with a dozen libraries with similar characteristics and you begin to understand the issue.