While the same should be true for us, many Christians simply do not take personal evangelism seriously. Another reason, however, and I believe the main reason why these cults are so successful, is that they are uncompromisingly united. They have a shared vision, a common goal, a singular purpose. And they go after their goal with unadulterated zeal. I believe that this is why they are so successful.
Unity is so very important.
The early church was a united church. They would exhibit a level of unity and oneness that will forever be an example and challenge to churches everywhere. In Acts 2 there is a lot said about being together. Every day they continued to meet together in the temple courts. They broke bread in their homes and ate together with glad and sincere hearts.