There are actually two reasons for this. The first is that education takes time away from the ministry. If they take time to go to college, that is time that can't be used to go in the ministry, and "lives are at stake". This is the excuse that they use the most.
The other is that they are pulling a scam. Anyone who is good at physics, biology, or astronomy will realize that many of the explanations pulled off by the Watchtower Society are impossible. For instance, the Flood water was supposed to have pushed down the basins, allowing the water to drain. But, in doing so, the water would have to push up heavier rock. This is like a thin child pushing up a fat one on a seesaw where they are the same distance from the fulcrum at the center: it isn't going to work.
Other science problems include the age of the earth. The Tower claims that man is merely 6,000 years old. It took only 6 days before that to make the earth, with each "day" running 7,000 years. This makes the earth only 48,000 years as of 1975 (today, the earth is 48,032 years old). And they bash carbon dating, saying it's off by whole orders of magnitude with no backing evidence whatsoever. Any seventh grade science student would know that radioactive matter breaks down at a reasonably constant rate, and this can be used to date something to within a few percentage points accuracy.
Then there is the demon issue. Many of those noises that they use the demons to explain away are actually from thermal expansion. If you are in a house in a quiet area, and it gets cold out on a clear night, the house is going to thermally contract. The interior will cool slower than the exterior, and this difference can make for some creaking noises. If there is heat running, the difference is even more pronounced. This happens most during fall months in arid regions where the temperature can be 80 during the day only to freeze at night. The creaking is not dangerous, but it can scare people that are not aware of the cause. And the Tower is eager to blame the demons. I have even seen a thread on this forum where Tupperware is said to bubble and pop open on its own after being taken from the refrigerator. Thermal expansion of the air inside is the reason, not the demons.
Aging is another thing that the Tower "Adam"'s away. Why do we get old? Not because of Adam's sin. It happens because of the telomeres at the ends of the chromosomes getting too short, preventing the cells from dividing. We are just beginning to understand that. However, I wouldn't be surprised to find it in high school biology text books soon, if it isn't already in some of them. Other causative and supportive factors will also be found, undermining the dented-loafpan theory.
No wonder the Tower wants people to stay away from college! They want children to be tired and sleepy during classes, especially Friday, so astute observers won't find these discrepencies in high school. This is probably why they want the children to spend evenings at the meetings, and the afternoons out in service, instead of getting homework assignments done. Too bad for them I was one of those who did well in high school science, and thus I can expose their secrets to any who might be inclined to look for the real truth.