And they do this on purpose. Children are not allowed to do anything in school that might make them independent of the witlesses. They are trained to pio-sneer or go to Beth Hell, not work. They are threatened with destruction if they do not obey. Everything outside is "from Satan". They are dragged to boasting sessions, and pressured to get baptized at age 6 (some make it to their teens, but too many get baptized in their single digits).
Then, once they realize the death threats are a scam, the threat becomes being disinherited. Their livelihoods are in the cancer. Their whole social network is in the cancer, because the world is "from Satan". Their families are loyal to the cancer, not the family. If they leave, or even express doubt about a minor issue, they are cut off. Even recruited witlesses can fall prey to this, if they fall into the scam of working for a witless or living with a witless (whether as a landslumlord or roommate).
Not to mention the fear of being hounded to death, which for some is worse than getting disfellowshipped. The witlesses will hound them to death for violations of virtually anything, using "brazen conduct" to force compliance. Even after they are disfellowshipped, they are not always left alone--one outspoken apostate has been hounded all too many times (one might say, once too many) despite repeated warnings to leave him the fxxx alone. And, for those with a few good friends, dorkhood is used to keep them at the Kingdumb Hell.
From a viewpoint of wanting a strong organization, it would be better to create obvious value. You would want to make people want to be in, and want to stay in by making it enjoyable to be there. While it would still start small, it would build--similar to the disco movement that started back in the mid 1960s and grew slowly until one day, someone incorporated a sample of it in a mainstream song. People liked it, so they began incorporating more disco into mainstream music. Not long after, disco became mainstream and eventually dominated. It eventually fell because too many people having no business making disco music started cashing in on it, making crap "disco" that barely qualifies as music (let alone as disco), and people got tired of that. To this day, good disco music still sells.
If a religion (or God) really wanted more power, it (or he) should have made the religion as much fun as disco music was in its day (and still is, for those unburing Daddy's old disco music). I don't think people need to be held hostage to something that is that much fun. By the way, disco still sells, despite listeners defecting to country, slow jams, soft rock, and hard rock/heavy metal. (And a good religion should survive despite its members going to other religions for a time.)