I’m sure some of that is the language barrier.

If you’re coaching Brazil, you pretty much need to speak Portuguese. Many of the players might have a passing familiarity with English, especially the ones playing in England. But many will be playing in Germany or France or Italy. So, the only real common language will be Portuguese.

Belgian players are most likely multilingual, speaking French, Flemish / Dutch and probably other languages too. Also, with the touchy cultural issues of Belgium, it might not go down to well to have a Dutch-speaking coach who wasn’t also fluent in French. But, if you have a foreign manager that’s less of an issue.

With England, you can be pretty much guaranteed that a large number of the players will be English-only monolingual. OTOH, there will be a lot of coaches who have a decent grasp of English, since it’s really the most common second language for international communication.

Argentina just doesn’t do foreign managers. There are other Spanish speaking countries, but if you look at their manager history, they’ve only had non-Argentinian managers twice, once in 1927-28 where a Spanish manager brought them to the Copa America win and an Olympic silver, and then again in 1934 where an Italian manager took charge for a single game (which he lost).

France isn’t quite as set on French managers, but it has still been nearly 50 years since the last non-French manager. And, in terms of languages, there aren’t as many countries to pick from where French is spoken.