There are many reasons why people consider self-publishing over the traditional route and this was covered in this post.  A further investigation of self-publishing may be needed for the potential author to understand the ins, outs, and type or self-publishing available to them.
The key distinctive characteristic of self-publishing is the absence of a traditional publisher.
Self-publishing [...]

For many authors just starting out, it can be a confusing and overwhelming decision whether to self publish a book or to seek out a traditional publishing house.
When it comes to publishing most people think of traditional publishing where the author completes a manuscript, writes a query or proposal, and submits it to a publishing [...]