That’s not true. I wrote the Panther book, Advanced Perl Programming, and easily made way more than 100k. Of the 25-30 or so dollars the books cost, I got 10% per copy, or $2 after taxes. The first print run of 35000 sold within the first three weeks.
The Camel book was already a huge bestseller, and was one of the anchor books of the early OReilly series. It made Larry a pretty penny