Because finding out that the research on "mind control" continued would be a big scandal, and in the past journalists like Gary Webb and Michael Hastings, who uncovered scandals about the CIA, did not to end well. Probably the CIA didn't kill them, but I'm convinced it contributed to mess up their life enough to disrupt their work. Intelligence agencies around the world consider themselves, rightfully or not, guardians of national interests. If a journalist works to uncover stories that could damage them, she/he may be end up being considered a threat not only to the agency, but also to national interests and that would put she/he at risk. Since there are not enough structures in place to let unjust behaviors on the part of intelligence to be scrutinized, researching on such things is not something I would do without also expecting ill-fated consequences.