Traditional publishing offers a number of advantages that self-publishing may not always provide.
First and foremost, traditional publishing offers established authors long-term book sales due to years of distribution and connections to bookstores, libraries, and other outlets. Also, when a publisher accepts a book, they often provide marketing and promotion of the book, which is often not available to self-published authors (unless the author is willing to pay for it).
In addition, publishers offer the benefit of their expert feedback and editing, which can be invaluable to a novice author. The publisher’s editorial team can help ensure that the book is professionally written and edited, as well as providing insight and advice on important topics such as book design and marketing.
Finally, a traditional publisher gives the author the benefit of their experienced staff in producing and distributing a quality book to a wide audience. A publisher will use their resources to place the book in many stores and venues that might otherwise be unavailable to the self-published author.
In conclusion, for authors seeking a more traditional approach to getting their book released to a wide audience, traditional publishing is generally the recommended route. The advantages of having the support of an experienced publisher, from initial advice and their marketing resources, to the expertise of their editorial staff, is invaluable.