1. "People will share a random Tweet from a thread" <- this is a feature. You can't easily address bits of a blog post unless the blog uses headers with easily accessible links that one can copy. Also, getting the broader context from a Tweet in a thread is pretty easy.
2. Blogging is hard. Not just creating a blog, but actually framing the content. Tweeting in a thread feels easier. There are rails. I can respond articulately here or on Twitter, but for whatever reason I always feel like my every attempt at blogging is miserable. I'm envious that the author of TFA finds it so natural, because it's something I'd really like to be able to do well. In the meanwhile, I have Twitter threads and HN comments.