Exactly. It's not just not-JSON, but it's obnoxious and hard to manipulate programmatically, on either end (client or server). That translates to a lack of too

Exactly. It's not just not-JSON, but it's obnoxious and hard to manipulate programmatically, on either end (client or server). That translates to a lack of tooling around it, an inability to write sane tooling, and difficulty interfacing in higher-order ways to things like interesting data stores. It's designed to be hand-written and parsed only with the official libraries.