I don't think the GB wants to mainstream for 2 reasons:
a.
they say they are no part of the world and constantly state that the differences between them and other religions is what defines them as the "true" religion.
b.
I am of the opinion that the Gov.Bod. are as much brainwashed by the whole machine as any members (i.e. I am not one of the conspiracy theorists who believe the people at the top have a different agenda) Therefore they believe they have been God's choosen people since early last century, that they are infallible and that no long term planning such as this is necessary due to the fact the end is very near.
(this last point also being the reason for their doctrinal blunders)