If you have followers on a twitter you have already built then it is just as important, especially if you have 20 million followers you stand to lose if twitter just decides they don't like you. For many it is your job, your livelihood, and your outlet to the world. For people and companies it may be the only way to reach out for collaboration with someone who you do not have a phone number yet and a twitter follower count is often used as a indicator that you are who you say you are, a filter of sorts. Since you can't go and meet every stranger in person elsewhere it is a requirement to have. Some people may not use twitter or only follow and never tweet but a lot of people use it as a necessity for communication, their personal well being, and businesses. Like it or not Twitter is worth billions for a reason and that reason is it provides a necessity for many that they cannot get elsewhere. The sheer size of Twitter already self-perpetuates their monopoly over that method of communication. It doesn't matter that you can go to Facebook if Twitter bans you. Take another industry for example such as TV. Disney bought Fox but was forced to sell Fox Sports because otherwise Disney would have had close to a monopoly on sports content as it already owned ESPN. Note it was not TV, it was only sports, a sub section of TV where they were deemed to have too much control. The internet monopolies just haven't had to face a determination of what is and isn't a subsection of social media but to be sure they are monopolies of public discourse.