They just don't communicate using JSON. I can see it now; Kernel JSON (aka kjson) support in the Linux kernel to attract Node developers.

Seriously I wish /proc was available as a tree of JSON documents as opposed to all these different ad hoc plain text formats. It would make using /proc a lot easier and more reliable

Could be unnecessarily costly unless the files are written ahead-of-time. I propose some kind of GraphQL-like interface to only read what you need.

/proc files are generated on-demand as you read them.

Generating JSON couldn’t be significantly more costly than the current ad hoc plain text formats are

Just take the Unix philosophy and replace the word "file" with "JSON file".