However, from my research I'll give my opinion.
First there was the Dianetics boom, a surprise to Hubbard and Campbell, and they tried to create Hubbard Dianetics Research Foundations, aka HDRF's. Note the word Hubbard.
That didn't work as too many Board of Directors and Hubbard wanted to be the only one.
The next boom was St Hill and creation of the Sea Org (where Hubbard was the only one via KSW 1965 as source of dianetics and scientology).
Next boom was in the 1980/90's with the recreation of Dianetics by marketing executive Jefferson Hawkins (books make booms). That fizzled out due to DM going crazy and then creating the hole and beating people and all those executives blew from the International Headquarters.
It's been on a decline ever since as there has never been a recreation of marketing and PR of dianetics and scientology since Jefferson Hawkins.
After 1980/90's the internet is born, and freer communication via early internet venues are born and come into existence, and ex members speak, as the internet and tech evolves, why we now have blogs and websites for free communication.
More Ex's speak out.
And here we are in the present moment with blogs, websites, tweeter, facebook, books, movies, you tube vids, etc galore talking about dianetics scientology. And even future books to be released by people as well as a tv show,
I'd love for David Miscavige to write a book.
Did I mention that most of the population of earth never heard of dianetic or scientology.
The indie and freezone movement of "the work was free so keep it so" are basing that idea on hubbard's idea of grass roots movement and word of mouth. Fail, as word of mouth is the internet and "no results" is what people will finally realize regardless of the initial hype by hubbard/scientology.
Dianetics and scientology are a marketing effort which is fail.