I know what you mean, but...I think they absolutely do think in this monolithic group-think with variation due to personal differences in temperament and intellectual training or capability.
Even though there aren't necessarily any "talking points" sent out by the DNC or anyone else, there is a huge amount of attitudinal and intellectual cross-pollination that occurs in the media world because they watch each other, and talk to each other. They may be in the same hotels, covering the same stories, waiting with time on their hands, drinking at the same bars or restaurants, and they talk to each other. They know, as liberals, how they are "supposed" to feel, and what stance to take on a given issue.
In an environment that is 85-95% leftist, they commiserate and conform.