Streams and resource forks are a play on a now-standard UNIX feature that almost nobody uses because it has a shitty non-file based API that also breaks most tools unless they are specifically aware of them: extended attributes. Resource forks and extended attributes are almost equivalent in every single way, except that extended attributes can only be read/written atomically (limiting their size to strings that will fit in RAM), whereas a fork or stream can be opened like a regular file. Stick that in your pipe and smoke it, UNIX sycophants, another case where Windows is more UNIX than UNIX ;)
The file-or-directory vagueness created by the hierarchy of resources buried within a file also more closely maps how the most popular path naming scheme on the planet (URLs) work: an URL can always represent both a file and a collection simultaneously, so I see this as closer to an ideal than the alternative where files can have no children at all. Sadly nobody actually uses these APIs like that, because all our tooling sucks so bad at coping with it. I sometimes wonder what the world would look like if directories on popular operating systems had simply been made 0 byte files