It falsely describes the deadly disease as something that will make children stronger. Cases of kids dying from measles in Australia are quite rare, because the country discovered science in the last hundred years.
Bookworld CEO James Webber originally said it would allow controversial content unless it was actually illegal, but in the wake of a vehement response from customers the company has changed its mind. Not pulling a book over controversy is certainly a legitimate ethical and business stance to take. Being responsible for harm to kids is probably not worth the risk.
Controversial anti-vaccination book removed from sale - News.com.au