The publishers of an eBook are able to override device settings/preferences.
Sometimes they do this because they feel it is important to the presentation of the work.
Sometimes this is done in order to make the ePub display correctly/consistently on multiple readers from multiple manufacturers.
Unfortunately I think that most times they do this unintentionally just because they are unaware of all the options available in eBook creation.
Thank you for the information. I suspected that might be the case.