The value is in having everything speak a common standard. In unix, that 'standard' is lines of text, which is inherently linear and lacks the ability to idiomatically represent hierarchy.
Conceivably, one could use modern serialization formats or we could do something a bit more interesting, like supporting some notion of "objects" directly in the operating system or runtime (in the case of powershell, the "runtime" is the .net vm; in unix it's the OS).
Such text can be parsed by both human and computer, because computer can just jump from field to field without parsing everything in between, like humans do.
Conceivably, one could use modern serialization formats or we could do something a bit more interesting, like supporting some notion of "objects" directly in the operating system or runtime (in the case of powershell, the "runtime" is the .net vm; in unix it's the OS).