Because Apple is evil.
I used to be an apple guy... had a macbook, multiple Ipods...
I finally got tired of paying their luxury brand prices. To be fair, for years, they were head and shoulders above the rest. Android has finally caught, and in some ways surpassed them.
But it was DRM that really hacked me off. I got my first smartphone , an Android (because of price, and lack of a 4g Iphone at the time), and was hacked to find that all the Itunes music I had bought (quite a bit over the last 10 years) will not work on it.
I wrote Apple customer service, and was invited to pay about $500 to upgrade it all to ITunes Plus. I told them to go to hell, and that I would never buy an apple product again. I sold my Ipod the very next day.
I then spent about 4 nights in a row burning all my Itunes music to CD's, and reimporting it. That circumvents the DRM. Have you tried that for your audiobooks?