I haven't self-published as I was lucky enough to find a small indie publisher. Yet, I very much see that other people choose to do so. Some have been very successful. Interestingly, some traditionally published writers have gone on to publish later books themselves. Some of the arguments are about control over their work, receiving almost all of the royalties but, crucially, I think, about marketing.
One of the changes and eye-opening changes at that, in traditional publishing, is that an awful lot of the marketing is up to the writer. This is one of the single biggest changes in a rapidly evolving industry. I keep saying that publishing is changing and many writers have come to the realisation that the option of sitting in front of your screen and living happily in your head is only something you can do some of the time! Traditional publishers only throw money and time at a small number of their writers - a fact of writing life today.