Also where are you getting your numbers from? How do you know that 50% attend?
So lets just say that out of all Mormons (15million) 50% attend at any given time then that means that 7.5 millions are actively going.
Now we know that not everyone is required to preach in the LDS religion. Only the missionaries go door to door. Perhaps this is why you "feel" you dont see them.
According to wiki about 80,000 are full time missionaries and 272330 converts in 2013. That means each missionary converted 3.4 people! Can you imagine if JW were this efficient or if every mormon was required to preach?!
So in conclusion, Mormons not only do so much more with so much less they also provide so much humanitarian aid to everyone (hell they were willing to help me paint my house!! haha) something that JWs do not do.