Most publishers don't hire proofreaders anymore and haven't in a long time which is why virtually all books these days have all manner of errors in them. The reality is the only thing a publisher can offer is contacts and advertising. And that makes the difference in most cases. Plenty of self-published people out there that no one will ever hear of beyond their friends who were obliged to buy their book.
"During times of universal deceit telling the truth is a revolutionary act."