I actually don't think this is true. I mean, you literally listed four sites that instituted new policies, from advertisement restrictions to direct user bans, after the election.
I think that many people in Silicon Valley, and all over the country really, viewed the culture war as won. I don't encounter any Nazis in the course of my day, after all. If the ongoing march of liberalism and progressivism is inevitable, then libertarian business ideals like "letting everybody speak" are a safe luxury. If Nazis are a tiny minority and their candidate is going to get crushed in a landslide, why bother banning them?
It's different now. A lot of people woke up on November 9th asking themselves what they should have done differently. I certainly did.
Time will tell. But I am hopeful that people in the age of Trump will start awakening to their moral responsibility to fight for justice.
A lot of them aren't going nearly far enough and are instituting policies just to make it look like they are doing something, like Reddit. Reddit needs to mass IP-ban a huge number of users, but they won't so they're taking what can be generously described as half-measures meant to look like they're fighting the problem. Reddit is doing the equivalent of what Trump's proposed lobbying reforms would do: all of jack shit and maybe make it all worse. You can honestly say the same about Twitter.