The paramilitary personnel chose to conduct this just as a Miami Heat game was coming to a conclusion and traffic and people were clogging in the streets. And of course, no one knew this was only a show, and not the real thing. Again, here's the official story for the hopelessly hapless who believe it:
The training is designed to ensure that military personnel are able to operate in urban areas and to focus on preparations for overseas deployment. It also serves as a mandatory training certification requirement.