[MarMema]

As to why they are turning on him now, I do not know and most people probably cannot tell with certainty.

Now the Chicago native is in the unlikely spot of being credited with the rise of the tide that’s threatening comedy great Bill Cosby, after he took on the celebrated actor during a performance. Multiple women had been accusing Cosby of sexual misconduct for years, but it, too, bubbled beneath the surface with lack of evidence and no widespread attention. Until now.

"On Oct. 16 during a performance in Cosby’s hometown of Philadelphia, Buress uttered the words “when you leave here, Google ‘Bill Cosby rape.’ … That [expletive] has more results than Hannibal Buress.”

[SteveH]

Alternatively

I don't know what changed. I don't know why now. I can only guess as to what took so long. But I know none of this happens without Constand. She was the first to tell police that Cosby drugged and raped her. It was her case that made Ferrier, Green, and Bowman decide to talk. It's her court filings that still get cited over and over when setting the framework for everything Cosby is accused of doing.

http://deadspin.com/the-former-basketball-player-who-brought-down-bill-cosb-1661203971

To me on the outside looking in it seems to be a tag team effort, and a tag team effort is the one of the types of siege tactics that one might expect to be required to take down a rich and powerful legal adversary.