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.
Because like all churches, they make money from it.
Anecdote: I went to a charismatic non-denominational new wave evangelical thing in Maui, for reasons I will not explain, call it amusement. I paid particular attention to the pastor before and after the collection plate, and it amused me so much that I went back to confirm what I had first seen: that every ounce of his charisma (and boy was he loaded in that dept.) drained from his Animus as soon as the collection plate was full. He would disappear into the background to suffer the remaining service until which time he could count his winnings.
Why can't these cults just follow their own rules, why the hell are you trying to take ME to your miserable heaven.