You don't think that maybe their motivation was to get that information out to a wider audience, and not just preach to the choir here on FR?
I would agree with you on that - the wider the audience the better, generally speaking. I did acknowledge in my earlier post here (#142) that the Arpaio investigation, although not coming up with much astonishing when viewed in the light of previous investigations, gives findings the official imprimatur of a law enforcement agency, which is likely to influence some people who previously were unsure about the birth certificate issue.