Really? Doesn't seem like it worked out well for them during the last elections, given that people like Dustin Moskowitz and Larry Page were directly supporting and assisting the DNC campaign (with others assisting the campaign less directly).
If they haven't done it (yet), it's only because they've decided not to (so far).
[1] https://www.politico.com/story/2016/04/google-gop-convention... [2] https://fortune.com/2016/05/07/facebook-confirms-it-will-spo...
Just because they were giving some support to the Republican party, doesn't disprove my assertion at all.