Because they always support the establishment candidate, with 2008 being the only exception for obvious reasons.
That is true and I'm not sure that Obama was the exception. Obama didn't start ticking up with African American's until after he won IA, proving that he could win (but he also had picked up key endorsements inside IA). By that time Obama was at least in parity with Clinton with fundraising (if not past her). Obama also picked up many more endorsements during the primary, starting with Oprah but also Edward Kennedy and many others including rivals after they dropped out (Richardson, Dodd, and Edwards).
So while Obama was never as much of the establishment candidate as Clinton, he was never the true outsider ala Bernie. I think all of this added up to enough establishemnt support for African Americans to think he could actually win it and switch from Clinton to Obama. Even if Bernie wins IA and/or NH, I am not sure that Bernie will follow the same pattern, and so I think this time that AAs will stick with Hillary, and that means she will still win.
