there's no explanation for why certain actions or choices are made.
it doesn't make sense why phantomjs gets a score of 7 while chrome headless gets 8, or why phantomjs and selenium aren't considered headless browsers or automation tools. why the most common legitimate screen resolution is flagged as suspicious or why tools like curl or wget which download conten, are running javascript instead. they would be in a stack that checks ua server side, not in js