The problem is that they don’t have many benefactors. Rich right wingers don’t throw money into a toxic hole.
Ironically, if they did have moderation so it was just a Twitter with /r/conservative people and not the_donald people, it might be successful. BUT, if it was - it wouldn’t be necessary in the first place! Those people can just use Twitter!
Twitter’s moderation is so permissive that the only thing left outside is going to be toxic.