I think the reason DIM hasn't caught on yet is because people just don't know about it. If you want research on it try Metagenics, I know they have spent alot of money on its research. It is still new and, for the most part, being sold by doctor's lines [of supplements] such as Complementary Prescriptions and Metagenics, rather than sports supplements companies (although they are starting to catch on).
Also because it doesn't increase testosterone levels (that catchy phrase people like to hear) but rather frees protein bound testosterone, which increases the amount of free (available) testosterone in the system.
Beyond this, I have no idea, except that it's not gear, and when people have access to gear such things seem trivial. Also there are so many sports supplement companies out there scamming people by marketing things that don't really work as claimed, and maybe people are tired of that so they don't give new things a chance.