A few things that might be worth considering:
Where I live, many church leaders preach door to door. Especially Pentecostals, who are constantly inviting people to go to their church. Note that with Pentecostals, it isn't just the leaders who do this. All of them seem determined to preach to everyone they meet.
The Mormoms and 7th Day Adventists preach door to door, though their methodology seems different. They don't preach in their own neighborhoods. They treat it as missionary work.
Christadelphians go door to door.
Over a very long period of time, the Catholic Church has converted more people to Christianity than there are Jehovah's Witnesses in the entire world.
As others have said, other orgs are using other methods, like TV ads, to reach as many people as possible. They did not have TVs in Jesus' day, so that was not an option. Some have 800 numbers and post billboards asking people to call. Some put out ads in local papers, or send out flyers by mail. Note that this is less annoying than dealing with a pushy evangelist on your door step. Also, preaching is preaching--people who do it by other means, besides just door to door, deserve credit too. :-) Naturally, the Society puts emphasis on the door to door work because that's how THEY do it. Who says their opinion is the final opinion?
As far as proving someone's faith if literally "the truth," others will emphasize points that their faith does best in building a case. Look up any religion on Google and add the phrase "true religion" and you will find many articles that make the argument that the faith in question is somehow the one that is true. They can all claim it. But it doesn't make sense to use their own standards in deciding which (if any) is right, now does it? That's just too easy.