Most JWs only go door to door because they have to, not because they want to, they don't enjoy it, and are not good at it.
Door to door sales is very difficult in general. People are either not at home or are very busy and are suspicious of anyone coming to their door.
Most people either have a religion that works for them or are not interested in any religion.
Most people do not know what Jehovah's witnesses teach, and nothing people usually say at the door informs them. Most people think of them as magazine salesmen.
If people do know anything about Jehovah's Witnesses, it's that they don't celebrate birthdays and holidays and attend hours of meetings every week and have to go door to door every Saturday. Who wants to sign up for that?
Promises of a paradise earth seem unrealistic, the illustrations in the magazine of children petting lions seem corny.
If anyone is taken in by the sappy illustrations of shiny happy people, they soon learn that this paradise comes at the cost of the violent death of most of the earths population, which is not an appealing message.
The internet makes it very difficult for the Watchtower to hide their history of bad date predictions, problems with child sex abuse, and abusive shunning policies.