Because big tech companies are now at the point where they can pick the winners in democratic elections, if they choose to do so.
[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.
If they haven't done it (yet), it's only because they've decided not to (so far).