I actually think this is kind of an unfair comparison. For one thing, standing around advertising for ANYTHING isn't the same as entering into a task with a group of people that you're more or less stuck with for 10 - 30 minutes. Secondly, we're bombarded with advertising from all sources no matter what form of media we partake in. TV, radio, internet, gaming, even just walking down the street and seeing billboards and other random postings. Most people just want to get along to their destination and not have to talk to someone who's outside their current scope of interest. Doesn't matter if you weren't selling something, or that you were trying to raise awareness on a good cause. Your example here would be similar to people standing midway through the dungeon trying to tell folks that there's still hope for the Ala Mighan resistance, and they're trying to raise awareness of the suffering of the refugees.
Take an activity that you do with other people. Say, going to the video-rental store (Which virtually don't exist any more, but used to be a thing!). You're forming a group (Your family or friends) and going to the store to rent a movie. You all work together to accomplish that task, talking to each other about what movie you're going to rent, who wants to see what, etc. Now imagine doing that with three random people. The goal is to rent a movie. There's really no incentive for those four random people to socialize or even talk about movie preferences. They're just going to go in, pick a movie, then go their separate ways.
EDIT: Of course I just realized, like a total derp, that your example is actually a good example in-spite of itself! You're attempting to accomplish a task by raising awareness for your cause, so that's a group that you formed with people. I'm sure you socialized with the other members of the group in order to accomplish a task, rather than wordlessly handing out fliers to each member and sending them off. Granted, this is an activity that you can't really "DF" without at least SOME communication. Though you could get stuck going out with people who just want to get the job done and go home, which would be your DF Zombies, in this case!