Interviewers may be prejudiced toward religion, for example, which is why they may feel it is necessary to ask about church.
If they are religious themselves, they may not want to employ people of other religions. It is maybe difficult to believe that employers would discriminate on the grounds of religion or previous illnesses, but it’s something that is a reality for some companies.
Just remember that you don’t have to answer these questions, as they’re not directly related to the job you’re applying for.