It's a sad reality but some of the most popular social media out there is vote centric, which basically means it can and is gamed by various interests in various ways. You have among other things bots who are constructed to sway political opinion as well as industrial trolls.
There are also politically active groups i.e. gun rights activists or libertarian free market groups that all jump in early to down vote posts that are counter to their political beliefs thereby keeping them buried and out of public view.
It's important to be aware of this the next time you're watching something bread and circus oriented i.e (cute animal GIF) or a political view gone "viral". You might very well be seeing something else if these above mentioned tactics weren't in play.