It's a hard furrow to plough. Unless you hit the right spot with a publisher, that's even if you get to contact one, you might as well give up going along that road.
We've had many a photographer giving talks at our club, with the end objective being the sale and promotion of their latest book. When I look at their productions more often than not I'm amazed that the've even had the temerity to approach a publisher, let alone getting them to agree to publish a book! No accounting for taste I suppose.
Even if you self-publish, via Blurb for example, you then have to market and publicise the book yourself, that can pay dividends but don't look for mega sales. My biggest seller so far has reached the dizzy heights of the high 80's, so I'll not be rubbing shoulders with Don McCullin etc.!
P.S. I've bought 4 of his books, I bet he hasn't bought one of mine.