Well, I am aware that doing so is often just indicative of cognitive bias - pay attention to that which supports your preferred narrative ignore what doesn't. Am I guilty of that? Almost certainly - we all are.
However, the MAIN reason I like and share political stuff is that:
(i) I am also aware that in certain academic circles people self-censor on this stuff given social/peer pressure, and I'm afraid that brings out the rebel in me (I'm wired in such a way that if I feel I am under pressure not to say something, I'm more likely to say it), and
(ii) MOST IMPORTANTLY, because I am VERY sure that the dominant narrative across the media is very skewed to the right and narrow in focus, so feel I need to do my bit to get other messages and evidence out there and discussion going. It's about moving the Overton Window.
Here's something I wrote back in 2012 on this subject.