Soy milk compared to other bean milks Is there any reason why soy milk is so popular compared to other bean milks? I mean, there really aren't any other bean milks sold in grocery stores unless you make it yourself. For example, why not use garbanzo bean milk or pinto bean milk? Is it simply a matter of tradition or is there a specific reasoning behind it?

Take almond milk for example. The reason why it's popular is simple: it's typically less expensive compared to other nuts, it tastes good, and it's versatile.

But if you look at the price of soy beans compared to other beans, they are about the same price per pound in the grocery store. And soy beans taste pretty much just like any other bean, so it doesn't get any bonus points there.

If there is a unique property of soy that makes it truly distinct from other beans, please share.
Its all about protein.

Protein content (and to a lesser degree, fat) is what will determine the yield when making curd from milk. Obviously it is also important for its nutrition.

Soy has almost double the protein of most other beans. It is around 17% vs 9% for most other varieties.
http://www.healthaliciousness.com/articles/beans-legumes-highest-protein.php

Because of its high protein and oil content and high yield it has become an agricultural staple. Because of this, as saj14saj said, it is very inexpensive at an industrial scale.

For these same reasons it has also been important in Asian diets for centuries. Soy milk also has a tradition behind it that I assume would make it easier to market than other milks.