What insulates these companies from Charter challenges and civil rights challenges or actions under the US Code for deprivation of rights is that these corporations are private and not public entities nor are they public utilities. I do not agree with this, by the way, as when the founders codified freedom of the "press", they meant the actual press that printed paper. Each person should not be restricted from the use of the "press" to disseminate opinions. In practice the internet and that includes YouTube and even blogs such as Weebly which hosts this site, are the latter-day "press". People just cannot invent their own sites although alt sites such as BitChute and Gab are proliferating but none have the reach of Twitter or You Tube.
In my view, the only way to ensure that free speech is protected online is by making the internet and companies such as YouTube and Twitter public utilities. There will always be arguments around what constitutes violations of Terms of Service but this can be adjudicated more fairly in courts.
Other arguments to support regulating the internet as a public utility are in circulation and easy to find but, in my view, the speech issue is a compelling reason.