Those royalties may be lower than you would like, but they are dependable and can continue quite a while, if the product is good. Once the publisher assumes responsibility, you as a writer are free to do what you do best - write. You do not have to pay anyone anything. Not even your agent. He makes nothing until the money starts to flow, and the money stream flows toward you, not away.
Self-publishing is much easier, and certainly more respectable, than in years gone by. What the writer thinking of self publishing must consider is whether he will be effective as a publisher. Can he get himself onto the radio talk shows, arrange the tv interviews, convince reviewers at major periodicals to read and comment on his book? Will a Youtube video promoted on Facebook lead to significant sales? And while all theses details of promotion are taking up the writer/publisher's time, what happens to the next book? Will it ever be written?
Of course the self-published author can hang his book out there and get on with the next project, but will that generate a living wage? I don't know. All of my experience has been with various kinds of publishers, media houses, governments, non-governmental organisations, and such, all of whom paid me to write something. In other words, straight along traditional ways of publishing.