Honestly, you raise a good question. However, it may be well to mention history. Historically, the Orthodox Church hasn't really been in as fortunate of circumstances as say the Roman Catholic and Protestant Churches. The RC Church spread so far because it was the most powerful and influential organization in all of western Europe for quite a while, and thus was able to use its vast wealth, power and ties with colonialism to spread. Protestants were able to travel to the New World and thus develop almost unimpeded upon in the most powerful, wealthy nation on Earth, and thus likewise use their resources to spread their faith. But Orthodoxy? Really, what do we have? We've been in the hot-seat for the past 700 years. The only time we were ever really fortunate was during the Byzantine Empire era, and during that era, nearly the entire Middle East and Russia were converted, showing that we did in fact make evangelization efforts when it was possible. But then Islam rose and pretty much undid all of our work in the Middle East and made us a minority barely capable of managing ourselves, let alone make missionary efforts. Russia continued to spread the faith in eastern Europe, but then when the Bolsheviks took over, Orthodoxy in Russia and eastern Europe became oppressed as well.
Now, fast forward to modern times. We're in a state of recovery. We're picking up the pieces of ruin from the persecution and destruction we endured. We haven't quite reached the missionary stage yet. Fortunately, when/if an official, unified American Orthodox Church is ever established, we may finally see vast evangelization efforts someday.