Take a lesson from the cigarette companies...

From http://www.quittersguide.com/smoking-statistics.shtml
Ironically, studies show that the percentage of people that are low income and smoke is greater than the percentage of people who are at a high income level. If you consider the cost of smoking this is ironic, but many researchers believe this directly relates to the level of education one has received.  The percentage of individuals below the poverty level whom smoke is a staggering 29.9%. Subsequently, the rate of people who smoke that have completed more than 16 years of education is a mere 7.1 % as opposed to 32.6% among people who have less than 11 years of completed education.
What does this mean? Evidently (pun intended), keeping individuals uneducated will result in a membership more likely to keep contributing over a lifetime and recruit more contributing individuals (theoretically, like an exponentially growing pyramid scheme, though in reality the numbers aren't that great), while encouraging education will result in a membership more likely to leave and thus not contribute nor recruit anyone at all. The WTBTS has plenty of money and their formula has worked well over the years. Like the old saying goes, "if it ain't broke, don't fix it."

And yes, I agree that ego is a big part of it too as noted above...

For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring. - Carl Sagan