Higher education (typically a 4-year degree or above) teaches you critical thinking skills. They teach you how to correctly and objectively analyze data to come to your own logical conclusions. As opposed to primary education and trade schools (or 2-year degrees) which are more about teaching you a specific skillset, but not necessarily the reasoning behind those skills. In other words, advanced education teaches you how to think for yourself, whereas basic education teaches you *what* to think. Which is why the Society has always allowed for the attendance of trade schools. In fact, the Pew study indicated that Witnesses have one of the highest High School graduation rates in the country, but the lowest college education rates.
Critical Thinking is anathema to the WTS (and, really, all religion because throught history knowledge has always been the enemy of religion) because it eliminates Magical Thinking and faith. I have heard COs say that it is almost impossible to go to a 4-year college and remain a JW afterwards. This is very true, but not for any reaons that the WTS would publically admit - they usually blame parties, drinking, sex, drugs, etc. It's actually because when the Society's teachings are objectively analyzed using proper logical reasoning, the whole thing very quickly falls apart.
Mormons also faced the same problems, but they addressed differently. Instead of demonizing any pursuit of higher education, they created BYU, which Mormons are encouraged to attend for secondary education, where they can continue to be indoctrinated in Mormon theology and be surrounded by other believers who are all being socially pressured to follow the herd.