Because they don"t like or appreciate it when you ask questions exposing them. They shy away when confronted, or can't answer.
Yes, of course this 'ministry' has always been geared towards those people who just need to be fed cheap and simplistic answers to life's hard questions.
The world where info is hard to come by...we don't live there, anymore. All sorts of info (good & bad) is cheaply available, to answer ANY sort of need. Point is, there are even fewer folks out there, who are so destitute of thought & direction so as to make them likely targets of the JW 'ministry'.
As has been parsed out before, the 'ministry' isn't really about making converts. It's about keeping the believers busy doing what the cult says to do. Given that, the 'ministry' could easily become focused on letter writing, or the like, and it would neatly serve it's purpose for the cult.
It would give the Dubs their work/sacrament + association. It lets the elderly stay engaged. It lets folks dodge the awkwardness of cold-knocking on doors uninvited. Win-Win-Win.