FB profited off the violence and only started moderating once the situation became unsustainable from a PR point of view. The reason this insurrection happened is because people were fed divisive, outrageous and false garbage for years for "engagement"'s sake.
But its clear the reason they're treated different is because Parler took a black and white stance and FB is a value judgement and much harder to criticize.
Both Facebook and Parler ultimately have the same goals - make money out of people while bearing none of the consequences.
Parler is just very explicit about this intention, where as Facebook wants you to believe something different but actually only behaves differently as little as needs to maintain the illusion.
In this case, I respect Parler slightly more because at least they're upfront about it. Both are scum and both should go, but at least one is honest about their intentions.
Parler also happens to cater to a common enemy with no political ties or PR appeal, where as Facebook gives you the illusion of being the good guy, all while making money off the same people Parler wants to cater to.
I have seen no convincing evidence that Facebook and Twitter make good faith efforts to remove comments that incite violence, according to the letter of the law.
To me, it looks like they selectively moderate the views that give them bad press (ISIS) and enjoy the massive engagement that comes from the conflict.
FB is the reason why this event happened. People went there to talk with friends & family but were instead fed an endless stream of divisive, outrageous and false garbage to generate "engagement" for years. No surprise some of them went nuts.