Good question.
It's related to purpose. Purpose + Money.
WT wants money by accomplishing their purpose.
Their purpose is to control, micro management of 7mi of people around the world. And they want money doing that because it's their purpose.
Your question is the same of "Why Google does not make food?" or "Why McDonalds does not make software?".
They could turn the WT in a big fast food company if you think just in money. But they don't want to abandon their purpose in first place.
WT purpose: Listen Obey and Be Blessed. Control, control, control....