Because Unix's file metadata was traditionally very simplistic – and while many contemporary Unix-like systems do better–such as with extended attributes (xattr

Because Unix's file metadata was traditionally very simplistic – and while many contemporary Unix-like systems do better–such as with extended attributes (xattrs)–that feature came historically late enough that it has never seen anywhere near as much use as it would have had it been implemented earlier. I think the designers of Unix were (in part) reacting to some systems they'd experienced (such as IBM mainframes) which had very rich–yet complex, cumbersome and rigid–file metadata, and in reaction decided to make file metadata as simple as possible. The idea that you could support richness with simplicity (extended attributes as arbitrary name-value pairs, leaving the name and value format mostly up to applications) didn't seem to emerge until much later. I could be wrong about this, but I think contemporary Unix-like systems actually borrowed the idea from OS/2 (which in turn was possibly somewhat influenced by classic Mac OS resource forks)