I also have noticed that the well-educated witnesses tend to associate with each other and therefore it reinforces their willingness to stay. Some of them also "try harder" by pioneering and reaching out to show that the Society is wrong by saying worldly education will lead you away from Jehovah.
Also, some of them seem to be drawn to the foreign-language groups since they can use their mind learning a new language instead of just going to a mind-numbing english language meeting. Also, if they marry less-educated witnesses there might be a challenge to defend their education by staying in as well.
I know many of them that see the flaws but don't know how to get out or don't want to suffer the change in social status that leaving will result in.