Not every studio has triple digits of QA alone. This is still testing, with a different group of people. Just because there are pros doesn't mean there's always enough, and it is also a better idea to get feedback from people who didn't spend years or months on a certain thing and possibly see it with rose tinted glasses, an outsider is a bit more neutral, as a standard rule.
I'm afraid that most of the testing is under NDA, and unless the piece of info is disclosed explicitly by devs or Community Managers, it falls under the NDA. For now we only know the application process, and whoever got in, if they feel the need to share that. But do keep in mind these focus tests will focus on different aspects of the game, it's not one set test.