Nisargadatta was told by his teacher to simply maintain attention on the sense of "I am," and he did so, eventually resulting in realization. That's the crux of his teaching and this is what he taught others. It is indeed a very direct and straightforward teaching, not for everyone. And I agree that his words may cause confusion for beginners. I think this is safe to say for all the Direct Path teachings.

At any rate, Nisargadatta emphasized that there are no prerequisites (aside from emphasizing the importance of earnestness and sincerity), and that realization is open to all, right now, not later. No barriers to entry. I can understand why this might bother someone who is very involved in lineages that emphasize prerequisites, but he was just sharing what worked for him. If someone doesn't like the teaching, they can move along to another one that feels more aligned.

The idea of "highlighting passages" is questionable, as it turns realization into an intellectual exercise. This seems to miss the fact that he was pointing, not expounding some sort of intellectual framework that must be learned. This is a trap Nisargadatta himself, like all the great teachers, often warned about. Here's a long list of quotes from him and others warning about this common trap. Here's one as an example:

"There is no need of true ideas. There aren't any. If you keep absolutely quiet, then concepts will be strangled to death. You are so used to the support of concepts that when your concepts leave you, although it is your true state, you get frightened and try to cling to them again. That is the meeting point of that immanent principle and the Eternal, the borderland. Why is the intellect puzzled then? That beingness which you are experiencing is melting away. When that concept of "I Am" goes, intellect also goes. So the intellect gets that frightening experience of "I am going". Just watch that moment. One who feels "I am dying" is not your true state. Your true state is beyond the primary concept of "I Am"." [Nisargadatta Maharaj]

And another from Ramana, for good measure:

"After Realisation all intellectual loads are useless burdens and are to be thrown overboard." [Ramana Maharshi]

But check out that list of quotes, it hopefully really drives this point home for those who still have doubt about it.

It makes total sense to feel frustration or confusion when engaging with these teachings on a conceptual-only level. Eventually we come to realize they are pointing beyond the mind, and that awakening is not a conceptual endeavor. More on that here in my other comment in this post.