The only get donations for their campaigns. If tech companies give evenly to both parties, it wouldn't matter to politicians if those donations stopped. If one party gets more than the other, one party would gain, relatively, if donations became illegal.

So the story isn't quite complete without mentioning: It's mostly the Republican party that has stopped acting in ways that could be considered good for the country. It's gotten so bad they are actively trying to undermine democracy in every imaginable way, including opposing any constraints on campaign donations and even the regular application of the few safeguards left after Citizen United.