My point is that people can choose not to use twitter despite the network effects.

I don't not use twitter because I think it hurts twitter. I don't use twitter because I know using it will hurt me.

Any politician/business/service/whatever that only makes announcements exclusively on twitter simply won't reach me, and I'm fine with that. I can't think of a single instance where missing such an announcement directly on the twitter timeline would have changed my life in a significant way.