You're not wrong. Most authors of academic papers are not good writers. Perversely, regardless of where they are on the spectrum spanning from good to mediocre to terrible, writers' output is usually made worse when they know they're writing for an academic context—this is why most of the blog posts you're thinking of, with their informal language, make better papers than the papers themselves.
I wish there were a culture of (a) always writing a blog post to accompany any paper, and (b) rewriting historical* papers to make them more accessible. On the latter point, undergrads should probably be doing this for at least one paper per semester, despite the general expectation that they ordinarily do not deal with "research".
* Doesn't have to be distinguished ones; just any paper you come across and feel is too hard for you/your peers to follow without more effort than should be necessary, or any paper you thought was interesting but didn't get its due in public, or ones that did but have fallen out of cross-generational memory.