Do you really need an explanation of why a multibillion dollar company wasn't removed and why a fringe app was?
If a gang member and a methodist get into a bar fight, do you think the fair thing is for the bar to ban both gang members and methodists?
No -- it is entirely reasonable to treat fringe groups that foster fringe ideas differently than large diverse groups.
Facebook, Twitter, Youtube and Parler are all bars. The gang members (insurrectionists) went to the Facebook, Twitter and Youtube bars and got into fights. The Methodist (non-insurrectionists) went to Parler and did not get into bar fights.
According to you the solution is not to ban the bars where the bar fights took place but the place where there were no bar fights. It really makes no sense.