It seems we have a different definition of collaboration. I assumed that it meant communication between the parties. Publishing blog posts has many purposes, but dirrect communication isn't one of them.

"They are under zero obligation to create bug reports, file issues, check in on a chat channel, or contribute in any other way to an open source software project that does not employ them." Correct, and absolutely fine, but not collaboration.

"Writing blog posts is a perfectly reasonable and normal community behavior." Correct, and absolutely fine, but not collaboration either.

"The members of the Zig project are free to reach out to the author!" Yes, but it's much easier, more efficient and direct for the author to have reached out to the Zig team.

"When you create a project in public people will write about it, tweet about it, complain about it, etc (if you’re lucky!)." Yes, but, once again, this isn't collaboration.