1, I believe Twitter downranks link tweets in the algorithmic feed. If your following is on Twitter, you need to meet them where they are, but you can't meet them with a link. I've seen some people work around this by combining a Twitter thread that summarizes the post with a link at the end of the thread to the actual post, but then you need to write twice (or 1.5x, I guess) the words.

2, thread-tweeting can be lower barrier than blogging. The tech side (hosting a blog and associated yak care) a little, but mostly the writing. Writing a big post all at once is a thing and easy to get discouraged by, where on Twitter, the lack of an edit button forces you to go forward and not second-guess yourself. It's also more ephemeral, less feeling of "this needs to be perfect since it will live on my website forever".

2.5, There's a retro-tech thread tweeter (who I'll avoid naming since they've requested to not be linked from HN due to this recurring complaint) who's said they specifically find it helpful for ADHD since they can tweet out bursts of little updates, work on something else, then come back. Personally I also have ADHD and trying to write a twitter thread is my personal hell, but to each their own :-)