1. Each sentence is its own tweet, and thus can be starred or retweeted on its own. This lets certain 'key ideas' or 'best lines' in a tweetstorm go viral, and brings interested readers to the full tweetstorm that otherwise wouldn't have bothered if they weren't hooked by the best part of it and had to see a full paragraph or blog post. When scrolling, you can also see the parts of the tweetstorm that got the most likes.
2. People can reply to different parts of the tweetstorm, creating subthreads, allowing useful discussions to branch off of different parts of the tweetstorm.
3. By forcing people through a clunky UX, you still force them to condense their ideas. Most writing is much longer than it needs to be. For example, I think most books I've read would improve by being 10-50% shorter. Twitter for sure has downsides, but it is nice to have at least one writing platform that errs on forcing people to the side of 'too short' rather than 'too long'.