almost all authors have had to do their own promotion since always. philip greenspun wrote about his experience (in 01997) with how publishers 'cover promotion' in https://philip.greenspun.com/wtr/dead-trees/story.html (content warning: not safe for muslims, page contains nude photography)

The only computer book authors that I personally know are Nicholas
Negroponte (Being Digital) and Michael Dertouzos (What Will Be). When
these books were new, they were in a big stack at the front of every
bookstore in the United States. The authors were interviewed on the
radio, on TV, in magazines and in newspapers. Any American who might
conceivably have wanted to read either book would have been forced to
at least look at the cover.

So I waited by the phone. Nobody called.

I went into Wordsworth, the bookstore in Harvard Square with the
biggest nerd book collection. They carry every “how to program HTML”
book ever written. They carry a bunch of Web/database titles by
authors who don’t know SQL. My friends would go into the store and
say “I’ve heard great things about this Greenspun Database Backed Web
Site book. Do you have it?” No. “Is it on order?” No. “Can you order
it?” Yes, with payment in advance.

My friends at MIT Press had ordered 50 copies for their little
bookstore and wanted me to come in and sign them. A signing! Just
like real authors. So I went down there every day. No books. MIT
Press had ordered their books a month before publication date to be
sure that they had it as early as possible. Two months later: no
books. The store manager had sent Macmillan a couple of FAXes and
made three phone calls. Finally, Macmillan answered “Oh yes, we
decided that you’re too small for us to deal with. You’ll have to get
the books from a distributor.”

My worst humiliation was in New York City (whose isn’t?). Here’s how
I described it to my brother:

> I was walking down Columbus Avenue with my friend Bobby. His literary
agent also represents Saul Bellow. Despite his credentials as a serious
novelist, he loved the copy of my book that I’d given him and, as we
walked by what is allegedly the largest Barnes & Noble ever (across from
Lincoln Center in Manhattan), Bobby said “Philip, let’s see how B&N is
presenting your book. I’m sure it is going to be huge, not like
literary fiction.”

> [Background: last time Bobby had a book at B&N it was on their 10 best
sellers list and copies filled an entire front window.]

> In the computer section, they had a table out front with a bunch of
Internet books for people who couldn’t figure out what those nine
buttons at the top of the Netscape browser do. They had a massive “for
Dummies” section behind the table. Behind the “for Dummies” section was
an even larger “how to program HTML” section.

> They had a big Web site design area with Dave Siegel’s book. Right
underneath was a two-shelf Web/Database design area. They had a big stack of
IDG’s “Creating Cool Web Databases” (the book I kept on my coffee table
as a joke), presented cover out. They had some better books. They did
not have my book.

> Nearby, Barnes & Noble also had a big database section. It did not
contain my book.

> We asked the clerk. He looked up the book in the computer. “Ah yes, we
have one copy. It is in the network section.” So we walked across an
aisle to a completely non-Web non-Internet non-database area of the
bookstore. There, among books describing the TCP/IP protocol (something
you don’t need to know about unless you are writing your own copy of
Unix or Windows NT from scratch), was one copy of my book. Spined.

> If a person walked into that store knowing that he wanted to build a
database-backed Web site, he would have never come within 20 feet of my
book. I don’t know if Barnes & Noble uses a central computer system
but, if they do, I imagine that all 700 copies they ordered are in the
wrong place.

My brother promptly wrote me back that he’d gone into a Barnes &
Noble in Washington, D.C. and found my book in the network section
there as well. I stopped going into bookstores.

When the dead trees world lets you down, you can always turn to the
Web, no? So I visited the The Macmillan Computer Publishing Web Site
and clicked on “what’s hot”. My book apparently wasn’t. But they did
have a nice banner ad for Scientology: “with Scientology technology
you could understand the purpose of life and through understanding,
achieve the goals you set out.” Using the search engine, I managed to
find a generic page for my book. There was no link to my Web site, no
sample chapter, no scan of the cover, no blurbs from the inside
cover, no author biography (just to list a few of the things that
were actually in Macmillan’s possession). This was on July 4th,
almost three months after my book was completed.

I’d talked to Macmillan earlier about them running some
advertisements for the book. They said “typically, if a book is
selling well after a few months then we think about running ads.”
This plays into my theory that publishers don’t read books. It is
easier to hire 10 losers to write 10 books on the same topic and pay
them each $10,000. Then they dump all of these books into the
bookstores and let the public sort it out. After a few months, their
inventory computer shows them which of the 10 books is selling best
and they get behind that one. Wouldn’t we all be better off if the
publisher paid a skilled writer $50,000 to do a good Perl/CGI book
and then actively pushed it?

Anyway, Macmillan apparently puts almost all of its efforts into
schmoozing bookstore buyers and cooperative advertising with
retailers. So the chance that an author would see an ad for his own
book is minimal.

One thing that worked great in the case of my book was sending out
promotional copies. We shipped out 100 three weeks after the book was
printed. Almost everybody read it. Almost everybody who read it loved
it. Almost everybody who loved it recommended it to several
friends. Almost everybody who recommended it to friends also wrote a
reader review at amazon.com (more about that below).

that was pretty much my experience with getting greenspun's book too in 01997. i went to my local bookstore, which had a really extensive and excellent computer books section. they didn't have it, but they did buy it from their distributor for me, and when it arrived, i went to the bookstore to pick it up. i don't remember if i had to pay in advance; i don't think so. so greenspun probably wasn't exaggerating at all

as for self-publishers, canonically they don't get royalties, they just get printed books from the printer. then it's up to them to sell the books