I've seen much bigger, though technically that wasn't valid json, but rather structured logging with JSON on each line. On the other hand, I've seen exported JSON files that could grow to such sizes without doing anything weird, just nothing exceeding a couple hundred megabytes because I didn't use the software for long enough.

Restricting the input to a reasonable size is an easy workaround for sure, but this limitation isn't indicated everywhere, so anyone deciding to consume this random project into their important code wouldn't know to defend against such situation.

In a web server scenario, 2GiB of { (which would trigger two overflows) in a compressed request would require a couple hundred kilobytes to two megabytes, depending on how old your server software is.