why did a new project have to be created to do the billing export to Big Query?
I believe it was done for a number of reasons. First, the initial project was created automatically when the free trial was started, so this serves as a demonstration of how to create a project. Second, it was intended to drive home the point that all resources are connected to a specific project. By making a new project, we can now put the BigQuery dataset in a targeted project and not just the default. Hope this helps.