As I sat with a fellow writer awhile back, he recounted to me a conversation he had with a traditional publishing house acquisitions editor. My friend was submitting a nonfiction book proposal, and the editor made a point of instructing him to include his platform.
When my friend asked if his proposal would be considered if he didn't include platform information, the answer was no. The quality of his writing was not in question; his platform was.
At that point, I turned to my friend and asked, "Is the quality of your writing any less good if you don't have a platform?" The answer is no. It may simply mean he isn't good at building a platform. The book may be incredible, life-changing, earth-altering. But if he doesn't have a platform...oh, well.
And that is exactly the argument for self-publishing. One size doesn't fit all.
Here is the truth: Traditional Publishing is a business. They must ask, Is this book good for our business? If it isn't, they will go out of business and there will be no more books from that company. But that model Doesn't work for all authors.
The self-/indie author asks a different question: Is this a good book? And, just like the traditional company, they must ask this—otherwise, they are in danger of putting out junk.
Two different questions; two different paths to publishing.