Why do you think that? By which I mean, what logical basis do you have for believing that? At what point, anywhere, in Jewish Theology, Catholic theology, or Christian theology, is it ever suggested that God makes things easy for us, or that he doesn’t require us to look to each other and to intense study to come to a greater understanding?
Why should it be self-evident? If Satan, who saw the fullness of God, could reject him; or Adam and Eve, who lived with a near-perfect understanding of God, could reject Him; why do you think that it being self-evident would improve the likelihood that people would adhere to it? Quite the opposite, it seems to me just through my own life experience that it is the struggle to know the truth that gives it its value. We work and study diligently to understand our faith, and it is through this hard work that we come to understand the importance of what we are learning.
Something easy isn’t worth doing, and nothing worth anything was every truly easy to understand. Throughout your life, it is always the things you truly worked for that give you the most pride, and seem to be more important. The same is true of the Faith, and the deep understanding that can only come from a lifetime of study.
Also, I’d like to point out that, when it was written, it was obvious on the face of it. That is because it was originally written for the culture in which it was written, a culture that is, with very few exceptions, completely foreign to us. Claiming that it should be obvious to us is like saying that every human being should have an innate and obvious understanding of latin, it’s a ridiculous claim because society has changed, and because latin is no longer the primary language, similar to how tribalism is no longer the predominate cultural construct.