Not familiar with the situation in Brazil, but it could be as simple as local credit being harder to get than global credit, or a desire to deal in a denomination that local credit doesn't typically offer without hitting a conversion fee.

A local farmer could perhaps figure out how to contact a swiss banker all on their own, but it would be a lot easier, and cheaper, if there were single place (or better yet, a few competing places) that offer a central place that anyone looking to use/supply credit could come together.