Three reasons: timezones, language barrier and legal barrier. First two are clear. As for the last one, if you do anything remotely important and sensitive to your business, you don't want a dude from Bogota to have access to your project.

Edit. I should add that if your project really matters, the dude from Bogota will be a spy or a blackhat with nearly complete certainty. He will be well spoken, likeable, presentable, competent, he will even appear to believe in your company values and will ask for a very moderate salary. And you will brag about how you've got such a superstar for 10% of going payrate here, except that one day he'll stop responding to emails after having collected all the info he needed.