You don’t just ask on the forum to be in the beta. There’s a beta sign up link that you have to use. And then you wait and hope that you get added. They already have a large number of beta testers, so they might not add more before launch.
Edit: as @kevistraining pointed out there’s a new link that allows you to request early access, whereas it was closed beta before. That probably means they are taking most people that request it.