I have several friends from grad school who have been published and have been VERY successful in different ways:
--One won major literary award with a cash prize that is more than most literary authors will ever make from book sales. They have not published much since. If you gauge success by impact, then this author is successful and may be satisfied with their success.
--One has been published in almost every major literary journal I know of, and got a two-book deal with a highly esteemed elite publisher after being contacted by an agent who was wild about their writing. The publisher made my friend's first book their big push--meaning, they promoted the author as a breakthrough writer, the book as a major, important work, and they put a pretty significant amount of money into the promotion. Unfortunately, the books did not sell very well, and now my friend has been downgraded to a non-priority by publishers because of that. They only made money from the two-book advance, not sales, and the total was under $15,000, from which the author had to pay some promotional fees, including travel and lodging. If you gauge success by how "important" the imprints that choose to publish you are, then this author could retire and be regarded as having had a brief and notable writing career.
--And one was published in oddball lit journals and had a couple of books published (I believe without an agent.) by a small university press that is not typically associated with 'important' writers. This friend's career stumbled along as they taught creative writing at a university, and suddenly their writing caught on a couple of years ago (It's brilliant.) and they have won MAJOR prizes, have sold big, big, big and have been featured in the most highly regarded mainstream publications--not only book reviews (all A+) but also author features. This author is a success by every measure I can think of.
So to sum up, one of my friends entered the publishing world like a firecracker and then basically stopped producing. Another was greeted by the publishing world like royalty because of beautiful prose, but did not sell well and was summarily dismissed by the publishing world. And another was "a nobody" whose slow-and-steady progress eventually became known to more and more people like a burning fuse and then blew up like a fireworks grand finale.
The publishing world is enigmatic to me. But the bottom line is the bottom line: publishers are story factories. Stories are their products. Major publishers exist for the same reason any business does: for profit. So they're all about sales. Fiction and nonfiction are approached very differently by publishers, and I get the strong sense that (despite what editors say) in almost all cases, nonfiction books are sold based on the renown of their authors, because the more connections they have to promote and sell books to, the greater the profits, and that is what it's all about.