[kstenerud]

Because there isn't anything else in this space that:

- supports ad-hoc data structures or schemas per your preference

- supports all common types natively (doesn't require special string encoding like base64 or such nonsense)

- supports comments, metadata, references (for recursive/cyclical data), custom types

- doesn't require an extra compilation step or special definition files

- Has parallel binary and textual forms so that you're not wasting CPU and bandwidth serializing/deserializing text. Everything stays in binary except in the rare cases where humans want to look or edit.