It is (or was for a long time, IDK) a strongly recommended practice from ICANN. I imagine nearly all countries to do that.

There end up being some weird edge cases where there are some countries which have both the equivalent of .co.uk but also allow registrations directly under the two-letter country code as well. .mx is one such case where most business are, e.g., costco.com.mx, but it’s also possible to register directly under .mx as well so Toyota Mexico is toyota.mx and not toyota.com.mx (the latter is registered, and ostensibly to Toyota, but the whois and nslookup records give very different results and the website doesn’t load when I try to visit it).