What @Gacee says is absolutely true, but beyond that I think the issue is that at early levels getting a bit of handholding to convey the “essence” of Japanese is in order, something that’s not really about any specific grammar point but more about the general concepts and introducing them in an order that makes sense.
Early on Japanese is really overwhelming for most people I think. I speak several languages so I know the drill when it comes to language learning, but I admit that I was still quite flabbergasted when I started learning Japanese with my usual methods (all the other language I’ve studied are Indo-European).
You have the complex writing system, the grammar is very alien, the vocabulary outside of katakana words is completely exotic and opaque. So where do you start? Should you start memorizing kanji? Or just vocabulary? What about grammar? How good is knowing grammar if you have zero vocab anyway?
Bunpro offers grammar and now vocabulary (but not really anything for kanji) but it doesn’t offer this content in a “holistic” way. It’s more of a reference than a course. References are great, but for complete beginners they’re just a bit hard to use effectively. Look at genki-style textbooks on the other hand, they offer lessons that each introduce some grammar, vocab and kanji while building on top of the grammar, vocab and kanji from previous levels. It’s a lot more guided.
I think if Bunpro wanted to offer a completely stand-alone Japanese 101 course it would need to offer some N5 deck that would contain both grammar and vocab (and ideally Kanji). And you’d have to take special care not to use not-yet-taught vocabulary in grammar points (or they would need to be keyed).
Also if the idea is for bunpro to work as a stand-alone ressource for complete beginners, it needs to have hiragana/katakana decks. Yeah, it’s boring and lame, but we all had to go through it…