I don't know if it is the case in Belize, but many countries have for decades operated differing schemes to ensure they won't be left with destitute visitors on their streets. Ensuring you have a return ticket is just one of these. The USA started the trend of shifting the responsibility for this onto the airline that brought the person in, so if an airline is faced with the possible sanction of having to carry someone out of a country for free, they will do what they can to minimise that likelihood.