I appreciate addressing this question directly from the perspective of arguments in favor of the practice. It basically answers the question of "why". However:

None of these reasons seem to address the problem, they just offer an apologia of sorts. The practice is still poor communication in my opinion.

The reasons are largely focused on the writer, and not on the reader. It says a lot to me. Even the reason "because people are on platform X" seems still focused on the writer getting attention, and not on the readers per se.

What I've never understood about any of this is if you're going to bother to write a multiple-post thread, why not just put it on a blog, and put a link to it on a shortform platform? Then people get a summary and a link for further reading, and you get to read the content in the best form for it. This is the purpose of URLs.

I can't get over what seems to me to be this weird stockholm syndrome phenomenon when it comes to putting longform writing on shortform platforms. All of the reasons given seem like legitimate reasons to use Twitter or Mastodon for something, but not for posting longform content on there per se.