[The LORD did not set His love upon you, nor choose you, because ye were more in number than any people--for ye were the fewest of all peoples-- Deuteronomy 7:7]
If the truth of Judaism is so blindingly obvious, and I'm convinced it is, then one may wonder: why are so few people Orthodox Jews? Out of a human population of about 7 billion, merely about 2 million are Orthodox Jews. (Interestingly, this number has been more or less constant throughout history.)
I think the first answer is that people dislike sacrificing even when they know that doing so will be good for them in the long run. For example only about 3 percent of Americans make serious efforts to have a healthy lifestyle. Judaism requires more effort than being health conscious and the rewards are more abstract.
Secondly,Judaism discourages converts. We certainly don't make all sorts of proselytizing campaigns and holy wars. We are a little like the United States Marine Corp. We want a few really committed people, not a mass movement of half baked individuals who can't handle discipline.
Thirdly, a large segment of humanity, perhaps the majority of mankind does accept Judaism - to some degree, in the forms of Christianity and Islam. All of these people agree that God created the world and that He gave the Torah to Israel at Mount Sinai, however they have distorted Judaism to accommodate their own pre-existing cultures and biases.