re: I expect the left to "go start their own Twitter"

Your premise is flawed in that you believe leftists actually want to get out there and create something of their own. They don’t. They would much rather someone else put in all the effort and then take it over like they do everything else. Take CNN for example, they didn’t create it but look at what they managed to do it. Same with Twitter. Twitter wasn’t created as an outlet for left wing lunatics but it didn’t take them long to turn it into what it became.