Self-published books: marketing = author's responsibility
Indie-published books: marketing = author's responsibility pretty much. Funds are limited in these small companies. They need a "unicorn" just as much as a tech start-up does. That is unlikely to be your book. To tell the truth, the indie gang don't know which of their titles it's going to be, any more than one of the giants like Penguin/Random House does.
Large Publishing House-published books: marketing = part of the deal struck, most likely, with the author's agent. The large publishing house deal used to include an advance if they were willing to take a risk on you. That's why it was so hard to get published. It must have taken a brave soul to risk 10,000 smackers of the publisher's money on a debut novelist. One would suppose that very few advances are paid outside of the Vlogger and Celebrity deals nowadays. I would think a story like Jo Rowling's (and it was no overnight success by the way) will become rarer and rarer in the future
However, it is easier to publish a book. Self-publishing can be done by anybody, and, cruel though it may be to say, whilst everyone probably does have a book inside them, in the vast majority of cases, that is probably where it should stay. In this vast flood of dross your book is bobbing about like a cork in the Atlantic. No matter how many tweets, hashtags, facebook posts, vimeo videos, or linkedin articles you post, that will probably remain the case.
Crowd-funding and indie publishing is also slightly easier. For a start there is a better than even chance that someone will eventually read a manuscript, this is the most fantastic fluke at somewhere like Little, Brown or Penguin/Random House. But the fact remains, that your indie-published book, however good it is, is no more than a slightly bigger cork and it's still in the ocean of books.