Privately owned companies cannot censor – governments can censor or not. Both companies have terms of use contracts/rules that users accept when they register to use the service. Violate the terms of use/service and you are gone. Same as baseball – if you break the rules, you’re out of the game – sometimes forever!
Although we find the censorship of the still-president of the United States sympathetic and fair, we must not forget that the world’s two most powerful social networks are actors with political and economic interests.