This would be a valid criticism if these companies didn't hire top tier operatives from both parties and donate substantial amounts via their PACs to both.
It's not clear why this would be the case. Why should we care which "party" somebody is from when then issue at hand is a revolving door between DC and the Valley? The military-industrial complex has done fine under a two-party system and so presumably will the private-public corporate surveillance state. Everybody in power in the US has to pick one of two letters to put after their name, but they're all part of the same ruling class.
Even if completely neutral with respect to the two parties, the effect of social media as a transport for political information means it has a high involvement in political activity.
Don't pretend those two parties form an ideal set of alternatives; they have many common problems maintained by their duopoly.
Do they? As far as I know the only example of any identifiably Republican person high up in Silicon Valley is Joel Kaplan, and we know from leaks that Zuckerberg spends a significant amount of his time trying to stop his workforce from lynching the guy.
