Why Does Ian Halperin Get into the Church of Scientology so much in his book about Michael Jackson?

Last night, I was reading Unmasked and was surprised at how much Halperin wrote about the Church of Scientology. I was also surprised at how much he wrote about John Travolta in relationship to the Church of Scientology. I know that Mr. Travolta is going through a very hard time after losing his son and wondered why this would be addressed in a book about Michael Jackson. Any comments would be appreciatiated