Getting back to the book. Roud sets out clearly early in the introducion what the book is about and then goes on to do that. If people want something with song texts then they know by a few pages in that they are not going to get them and why.

It does what it says on the tin*. If you want baked beans with little sausages don't by a tin that just says 'Baked Beans'.

*OK, so it may not be specific from the label but you can read a few pages of the Introduction standing in a book shop or get the whole Introduction for free from Amazon.