If it weren't for the filibuster, Democrats would have to do more than "talk the talk". They would have to actually affect legislation. If they do the right thing they will be targeted and challenged by big "Citizens United" money. If they cave in to corporate pressure and vote with the Republicans they can no longer pretend to be noble defenders of democracy. The filibuster provides them with the cover to have their cake and eat it. It just means the rest of US have to eat cake too.
Of course they're frightened to modify the filibuster. It's easy to vote for the right thing when you know no one takes your impotent vote seriously because it's not really any threat to the powerful interests. You can always rely on the filibuster to keep you safe.
Stepping out from behind the safety of the filibuster -- truly changing the rules -- will require Real Courage.