It's a specific representation of JSON-like data structures, with an indexed deduplicated binary format and JSON encoders and decoders. Why "nothing"? It's all about it.
Mostly it's not about streaming. More efficient streaming is a byproduct of the representation.
> because you can detect { and } and { and ] and " and ,
You need a pushdown automaton for that. In case of SICK you don't need potentially unbounded accumulation for many (not all) usecases.
> the values must be streamed first, before their location/pointers
Only to avoid accumulation. If you are fine with (some) accumulation, you can reorder. Also think about the updates.
But again, streaming is a byproduct. This tool is an indexed binary deduplicating storage which does not require parsing and provides amortized O(1) access time.