Jehovah's Witnesses and Mormons don't just go door-to-door to spread their word. They know that the extreme majority of people they ring are going to just shut the door in their face. Leadership knows this, and it's a tool. After they get repeatedly rejected, church leadership can say "They don't love you, but WE do!" and it further solidifies their belief in their religion.

It's all about creating another "us vs them" scenario.