I personally prefer to develop my own machine learning solutions. One may, of course, chalk this up to ego. However, in the first chapter, I introduced the notion that there are different types of problems. Some of these problems may be solved by machine learning algorithms. Some problems may only require general machine learning algorithms, while some require specialized algorithms derived from the general algorithms. In the majority of this book, I've shown the general algorithms, and readers are free to adapt these to their own specific problems.
I, too, recognize the value of having general machine learning algorithms as being part of the solution. Imagine that you are developing a program to reorganize your personal photos on your computer. There is no need to spend a protracted amount of time getting a convolutional neural network trained upon a corpus...