That’s because writing a JSON parser is pretty straight forward with just a couple edge cases.
Writing a conformant XML parser is a HUGE undertaking comparison.
I could get most places to give me the time to write a JSON parser in whatever language of it didn’t have one. I couldn’t do that with XML.
Because of this, every common language (and most uncommon ones) has a JSON parser while XML parsers are less common (and fully conformant ones are even more rare).