Exactly right. They are private businesses and such can have their own requirements. You "agree" when you sign up.
I would love to see Trump start his own site. Firstly he will be disappointed as he will quickly find out how many "Supporters" he really has. Then when he sees the quality and the content of these catfish noodling cretins he will realize that his follower base are likely meth heads looking for something to do. He will also then get to see what people really think of him because I guarantee you there will be a lot more "You are a fucking Idiot" posts then anyone who cares that he lost the election and it was all a set up. I say "Come on Trump you insecure loser. Set up a website"