Embedded system with limited bandwidth, the data was mostly simple values that did not really need escaping 99% of the time (mostly no unicode or control characters in strings, but still _possible_, and we needed the streamability of array-of-structs instead of struct-of-arrays.

Why not some binary format, then? Well, it's easier to debug and share the data with non-technical people (just open in excel or equivalent) without having to run a conversion step.