I find a surprising amount of value in in-band media type signalling. Not everything sees the declared media type, and media types are regularly calculated from file contents (magic numbers) rather than anything else, also. So here, the very first byte lets you know you’re dealing with a JSON text sequence rather than JSON or concatenated JSON or newline-delimited JSON or whatever else. It really comes down to just that. That line feeds are permitted (though largely not recommended) elsewhere is nice for human writing, but not particularly relevant, as these formats are not generally intended for human writing (you’d just use normal JSON if you wanted that).