I used to be when i was a kid. I can tell you why it is good for them.
We used to go knocking on doors all the time at the weekends (Preaching the word of God.) I know it is a pain but that is the way it goes but to them they have to spread the word of god.
Now for the dull bit.
some of them will try and achieve more hours between 60 -90 hours a month dedicating themselves to this
and finding a job that allows time of to do this is hard.
It has been said B4 Window cleaning is good lolly for the hours worked and your your own boss.
Now for the fun part. How natural is it to knock and canvass for your own customers.
Dudes I know been there and you are less likley to get abuse when u ask if they want a window cleaner instead of a new religion ;-)
Also is door knockers run by a JW

?? ;-)
Regards Jago