Unfortunately, the true and stringent editing services that should be provided by these companies (resulting in multiple improved revisions of text) is counterproductive to their main goal: getting people's books into print quickly. All "self-publishing" companies who do not require you to improve your "good" story into a "professional" story, is merely a vanity press in disguise. Their greatest fear is that if they require too much of you, you will simply do business with a different company. So, they make it easy to produce a mediocre book, rather than difficult to produce a great one. The price is the same for them.
When you self publish, you have removed the natural quality filters that competition with other authors provides. Too often this results in lower quality books. Face it, big publishers aren't the only ones producing crappy books; very few self-published books reach the level of "professional". You can, however, overcome this problem. Probably the easiest thing to do is join a writers group where you can exchange manuscripts for revision suggestions. SCBWI has manuscript sharing, and a few of the comment contributors are very good.
If self publishers want to be taken seriously by other authors, publishers, and the consumer, it is vital that we be diligent and ever-mindful in our attempt to produce truly professional level material. Always expect the very best from yourself, then verify that it is as good as you think. Revise, revise, revise!