I feel like you may have a right-skewed view of this issue. If you look at it globally it may be different, and I don't know where you're from. Here in the United States (where all four sites are headquartered) sites like Facebook/Twitter are moderated somewhat right leaning for their role in aiding right-leaning former president Donald Trump in 2016. He lost their support later due to his abuse of power but that's a bit out of scope of a HN comment.