If they didn't upload these things then they wouldn't be there for others to take, and people who want the books wouldn't even need to consider if they did or didn't want to pay for the book.
That is absolutely the issue. There's no way for those of us in the legal/moral grey areas to get what we want (short of paying twice) other than through using the illegal sites. And once stuff is up on there, there's no way to stop people with zero justification from taking the books just because they can. If the publishers offered a better and more open service, no-one would be able to defend these sites.
And... it's interesting how things work sometimes. You might have seen a recent story about the Playstation 3 having finally been cracked open and made able to play pirated games. It's taken five years for that to happen. Why? Well, when the PS3 launched Sony offered hackers and tech guys the option to install Linux on it and fiddle about with the hardware as much as they wanted.
Then they removed that option, and the thing was cracked within the year. I always thought the "we're cracking it so we can run homebrew software" when it came to games consoles was a silly excuse and everyone really knew it was about piracy.
But it turns out there's not that many people out there capable of cracking stuff like this, and if you placate them, just say "here's an open system for you to mess with, just leave the games alone" they mostly will. I'm genuinely amazed by this story, as basically the potential for the PS3 to be hacked was there all along, but it only happened when Sony pissed off the people smart enough to do it.