Facebook is whatever the user makes of it. It’s a tool that enables the user to share their comments, photos, links, jokes, events, etc, with multiple contacts, friends and acquaintances.
Here’s the thing, people use Facebook in different ways, for different things and don’t always agree with each other about what’s appropriate.
If someone chooses to shut out, ignore, or block opinions different to their own, then their feed will reflect that.
To apportion blame for an election result on Facebook makes no more sense than blaming the internet.