That's work-for-hire, which was the agreement that was offered to me. At no point was Penguin Books about to squabble with a spot illustrator for incentives on a book that no one speculated would even sell. My job was to draw 12 cartoons for a payout, and grant the rights to Jordan Peterson. The other alternative was to say No Thanks, which I ended up doing for the second book.
It's no different than doing Buy Out work for Marvel or DC. Dale Keown spent a year doing drawings of The Hulk for Marvel Entertainment to use on merchandise. There was one particularly famous image that ended up EVERYWHERE. For years, if you saw anything about the Hulk at Walmart or Target or at a theme park, it was this particular Dale Keown image. Beach towels, toy packaging, t-shirts...
He was paid what most people pay in a month's rent for it. And that's it. It's disgraceful.
The original art was a gift to Peterson. Had I sold it, I might have earned another $10K or so. But the real value in working on that book was having done it. People found me, and are still finding me, because of it. Many of them are buying CYBERFROG now. So if I want a Lamborghini, I can buy a Lamborghini.