So what's the point to go with them? We all can save it as a pdf and upload to Gumroad,or even send it to Amazon to print. I appreciate books on JAVA or Docker don't sell in millions but I'd at least expect the publisher to try to put my book on the shelves..

Good question. :)

It depends a lot on what the author wants to get out of it and what they want to do themselves. Going with a traditional publisher gives you:

* The prestige of your book coming out of a well-known publisher. If your goal is mostly to boost your resume or public speaking fees, then having an O'Reilly animal on the cover of your book can be very valuable.

* They provide developmental editors, line editors, copy editors, illustrators, and typesetters for you. If you don't want to do that yourself or find freelancers, that saves you from the headache.

* Likewise, they deal with the administrivia and legal stuff around distribution, translations, ISBN numbers, licensing, etc. I imagine they might provide some legal cover for you if you, say, defame someone in your text or use a copyright image.

* Your editor will create a timetable and some urgency for you to get the book done. That can be really helpful for people who have trouble summoning the discipline and structure to complete a book.

All of that stuff is valuable. The question is whether it's valuable enough for them to take the lion's share of the profit that the book generates.