There was a time when self-publishing your book through a vanity press was the kiss of death for any hope of a writing career. It was considered tacky and desperate, and not something any worthwhile author would ever consider. Then, with the self-publishing and digital publishing revolution, the notion of having more control over your work trumped much of the negativity surrounding the air of "desperation."
Eventually, self-publishing gained even more respect. Going indie for one title was a good way to earn some income while querying your other works; but that notion evolved even further to self-publishing your books only to have their sales figures and reader response prompt a traditional publisher to make an offer.