Its size has attracted a number of companies or 'significant' individuals that provide regular updates on activities exclusively through this platform. For instance SpaceX, Elon Musk, NASA, etc have chosen to use Twitter as a primary PR platform.

The reason these companies use it as a PR platform is obvious - there's a lot of users. I can't even fathom why it has lots of users though, at least not without mocking the state of society today.