"Noah didn't make many converts either. Does that mean that his preaching was a waste of time? No, because preaching serves a dual purpose.
It also serves as a warning that Jehovah is soon going to intervene in the affairs of mankind, and those who are not prepared for it will probably not survive it"
Well, that's one view. In my (no doubt) cynical view it serves as a tool for the WT organisation to keep 'the faithful' busy and occupied, 'up with the program' so they don't stop to think, and don't dare to challenge.
Just my opinion, you understand, I may be wrong.