It is pretty widely accepted hypothesis that politicians do not "corrupt" when they are elected to office but that corporations support politicians which favor their positions. Politicians that have money have legitimacy. Legitimate candidates get elected.
Couple that with the fact that corporations often donate to 50+ candidates (on both sides of the aisle) and not only do they have a pre-polling vote (through money) but they also get to play in many elections.
It's the house vs. the people and the house always wins.
I don't know if you've participated in the system, but it's not fair to equate that with a corporation donating its own money to a political campaign.
If anything, internet corporations are showing up late to the game.
If they saw that modern society could not function without them then they could then effectively hold legislators over a barrel and say "pass law X or we turn it off", these laws might not always be things we would like.
Of course if they pulled that enough times I'm sure another engine would come along and replace them.
This is a problem I have with centralized software and data that is proprietary to one company, I imagine Google and Facebook could legally do some pretty nasty things if they wanted to.