Not that long, browsers implemented JSON.parse() back in 2009. JSON was only invented back in 2001 and took a while to become popular. It was a very short window more than a decade ago when eval made sense here.

Eval for json also lead to other security issues like XSSI.

And why do we not anymore make use of it, but instead implemented separate JSON loading functionality in JavaScript? Can you think of any reasons beyond performance?

For IE7 support, yes... https://caniuse.com/mdn-javascript_builtins_json_parse