On Twitter, there is discoverability. As you browse, you frequently jump across profiles, and are continuously recommended users to follow.
On Twitter, there is brevity. In general, blogs are not designed for hundreds of short posts.
On Twitter, you do not have to pay for hosting, nor do you have to manage anything.
So there are a mix of technical, social, and network effects. Until these problems are overcome with a single solution, Twitter will retain its stranglehold on content.
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Personally, I wish Twitter would just remove post length restrictions and make it a proper micro-to-macro blogging service. (To be clear: I'm not a fan of a Twitter monoculture, I hate their UI, they make getting data difficult, their site is painfully slow, and they are often user-hostile. But it's been years and no micro-to-macro blogging service has overtaken them, and at this point it'd be better to have something dastardly that works, than something dastardly that doesn't.)