I think it's because Amazon holds most of the cards, so if you don't like it, you can go hang....
My figures (quoted elsewhere in a separate post). Sell my £24.95 book on lulu.com - I get ~£11. Same book on Amazon, ~£4. I did another book which I sold on both platforms, and firstly I had to raise the RRP to £7.95 so I'd make more than £1 on an Amazon sale, and secondly, I didn't sell the ~3x as many as I'd need to to make the same money as selling on lulu.com - so I now only sell the second-latest version of any of my main book on Amazon so that people will hopefully see that there's a newer version on Lulu and buy it from there.
My figures (quoted elsewhere in a separate post). Sell my £24.95 book on lulu.com - I get ~£11. Same book on Amazon, ~£4. I did another book which I sold on both platforms, and firstly I had to raise the RRP to £7.95 so I'd make more than £1 on an Amazon sale, and secondly, I didn't sell the ~3x as many as I'd need to to make the same money as selling on lulu.com - so I now only sell the second-latest version of any of my main book on Amazon so that people will hopefully see that there's a newer version on Lulu and buy it from there.