Progressive Politics

It could be a lot of things. Many events aren't open directly to the public. Sometime they fill seats by giving them away or giving priority access to certain groups or events. You don't generally have people walking up and buying ticket and even if you do it's not always shared in placed the average American would know to look. Best case, These are poli-sci students that went because a professor told them to.

My general guess is that on top of what I said above, this is simply an establishment event in an establishment town and so the audience is likely mostly establishment insiders and not the general people.