I think the answer to this question will be somewhat opinion-based, but my belief is that language teaching (whether L1 or L2) always contains a political component of how certain parties want you to speak / write. In this case of Japanese, they try to make foreigners speak politely -- thus they don't want you saying けど for "but" instead of が – virmaior 14 hours ago
I stubled on this book in my first few months in Japan and learning Japanese from scratch and it really did it for me. It will show you I think around 20 uses af GA among many other Particles. amazon.com/All-About-Particles-Handbook-Japanese/dp/1568364199 – Mark 14 hours ago
@virmaior I think it's less a nefarious cabal of JFL teachers trying to make non-native speakers into mealy-mouthed patsies and more the idea that the potential for disaster is smaller when you err on the polite side rather than the casual side. Especially in Japan. – Matt 8 hours ago