https://jekyllrb.com/docs/collections/ says the following about files inside a user-defined collection:

"If no front matter is provided, Jekyll will consider it to be a static file and the contents will not undergo further processing. If front matter is provided, Jekyll will process the file contents into the expected output."

If Jekyll treats assets in a collection as static files, why are these files not added to site.static_files?

I should mention that, in my project, the collection hash in _config.yml defines a few values such as output: true.