I tought that because most of the books are outdated (15 years on IT it's an epoch), albeit the sed/awk/perl/*sh and Sendmail books are still godly useful.
If you want these books very cheaply, the Perl CD Bookshelf usually sells for about $5 used. You get Perl in a Nutshell in print and a bunch of the other books on CD.
A better introduction to Perl these days is Modern Perl, which is available to read online for free or you can pay for a print book. http://modernperlbooks.com/
Also, there are legal issues over promotion of pirated content.
Also, there are ethical concerns over pirating content that is easily and cheaply available legally.
Also, I said "Please" and didn't force anything on anyone.
Also, under a strict interpretation posting directly to pirated material is likely a violation of the Terms of Use for HN. https://www.ycombinator.com/legal/#tou