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.
“That's it. You people have stood in my way long enough. I'm going to clown college!”