I'm not sure why that graphic excludes it, but they link to the source they're relying on, and they do seem to track it as well.

https://www.article19.org/gxr-22/#:~:text=Meet%20our%20teams....

> ARTICLE 19 Mexico has its own methodology for tracking the freedom of expression situation in the country – they are not included in GxR rankings or any country-level analyses using the metric.

Which I think means basically "for historical reasons they are special". Shame though, cross country comparisons are interesting even if they are hard to do properly

Also Greenland and a couple of other Central/South American countries.

It's probably just areas they don't have good or reliable data for.