There are ample other blogs out there in the ether that is the Internet (including some of my past posts) where the Belize-Mexico comparison is hashed and rehashed, I'm not going to replicate it here.
Moving anywhere is a major life event. Moving to another country, even more so. Not everyone is the adventurous type - by either nature or circumstances - so there is a great need by some to find some commonality between what was left behind and what is offered in the new locale.
Belize wins in two ways: language (English) and currency (stable 2BZ:1US exchange rate). This may not seem like much to some of us world travelers, but it is a very, very important issue for many who might actually be making their first move to another country. The (relative) ease of doing business, dealing with bureaucracy, and bonding with others all in a single, mother tongue make everything else that's not quite as desirable, at least acceptable.
Twenty years ago there weren't as many immigrants (or expats) in Corozal as there are today but that's to be expected...like attracts like. Wouldn't you rather move to a place that knows (or at least understands) where you are from, speaks your language, and can help you make your way in your new adoptive country? Of course you would.
Mexico wins in so many more ways as far as we're concerned. Varied culture, extensive history, inexpensive cost of living, and all the amenities of "back home" (unless "back home" was someplace like..oh...Belize. Hahaha, couldn't resist).
But one does need to be far more adventurous moving to Mexico over Belize. One must be open to learning at least the rudiments of a new language, experiencing a different culture, and prepared to deal with all of life's events, some simple and some complicated, in a strange new place where you're now a minority member. You might not have anyone to help guide you or even, at the end of the day, a sympathetic shoulder to cry on when the frustration is maximum. Yep, takes a certain kind of person to do that. No better, no worse than any other. Just different.
Vive la difference!