I don't think the Dem establishment is blind or deaf. They read the same polls we do. But they bought a ticket on the Clinton Express long before any Democratic candidate publicly declared for the presidency. Why? Corporate money for the party and favors for the loyalists. And besides, it's dangerous to stand up to the powerful Clintons, who never, ever, forget.
Because win or lose with Hillary, most of these party regulars will continue to maintain their position, their power, and their corporate sponsors. Life, as they have enjoyed it from their neoliberal stage, will go on, whether H or D is living in the White House. Oh, it won't be as nice with Trump, but it will be more than tolerable, because the status quo will be preserved. A Bernie Sanders presidency to them threatens the end of the good life, and they'll do anything to keep him from the nomination, even if it means the Dems lose the presidency. With Sanders, they will be exposed.
They know, they see the polls, and are reading their own internal tea leaves. They are nervous about her chances. But win or lose with Hillary, they'll still come out OK.