With a traditional publisher and a good book, you can easily get more than 4-6 times the sales. Sorry, gatekeepers can still be pretty effective, even in this day and age.
It's just like the equity equation. Also, being published once makes it easier in the future should you desire to go that route, while self publishing does not.
The way I see it, a writer self-publishing is like a hacker building his own servers and running them from his basement.
When you print on demand, your printing costs are twice as high per copy, but since there's no middleman, you make more as an author. Of course, it's impossible to distribute, so it doesn't really matter. It's only a good option if you really only intend to sell a few copies to friends and family.