Using Blurb or a small number of competitors in the "print on demand" business is simply a function of the authors decision not to make any investment in printing. Once a decision is made to make a limited print run, there are many more options available.
Personally, I rejected Blurb and other POD competitors who subcontract out the actual printing because of the print quality. I chose
Edition One Books in Berkley CA to make a print run of 100 copies of my book "Vignettes Cubano" because of their quality and reasonable price.
My approach was different as you cannot buy a copy of my book. If you are one of the 65 people who have a copy, it is because I wanted you to have one and gave it to you. My decision not to sell my book was based on my conviction that the very best I could ever hope for was to recover my marketing costs. That is no profit was realistically possible and an economic loss was probable even before considering my time invested. But I am a bit unique in photography and publishing circles being a MBA / CPA with a lifetime of business financial management. My publishing decision was based on a personal desire to better communicate the message of the book and to leave some legacy for family and friends (a/k/a enhanced self esteem)
These financial factors are based on economics and unrelated to the quality of the actual work contained in the book. Publication of Robert Frank's "The Americans" was not initially financially successful. If his talent could not pull it off at the beginning, I doubt that any of ours could.