Belief and knowledge are two separate things. How else would you explain that not all scientists are atheists? Surely you aren't saying that those scientists who have a personal or religious faith are uneducated. A recent study (2010) showed that of the 1700 scientists involved, with almost 300 interviewed, spirituality plays a part in the lives of almost half of that group. It doesn't mean the individuals are all religious, as in believe in a supreme being of some sort; they believe in a power greater than themselves and that belief does not directly conflict with their work.
Because the scientists were raised that way by their parents.
We all have a tendency to stick with what our parents taught us and to follow their example. Not saying rebellion doesn't occur, but if your claim is about people tending towards religion because of religion itself, then we should see a many more people choosing from the various religions available rather than sticking with the ones they were raised with.
Notice that this is also developed from a survival instinct. Young mammals will often observe their parents when they are young to develop survival skills before departing the nest. This is why, say, a bear surviving on garbage of a nearby town is not just bad because the bear may suffer, but because its cubs will learn that the only way to survive is rummaging through garbage.
It becomes even harder when rejecting a parent's belief may either anger the parent (disappointment and pressure to follow the way they were raised) or cause the child to stubbornly defend their beliefs out of an insecure fear that their parents raised them in a manner they find questionable (which would de-legitimize their parents in their own brain, even though rationally it should not affect their outlook on them). These examples are not a majority of the cases, but again, can influence people.
Basically, before most people even get to the point where they fail to separate their professional lives from their spiritual and have a personal existential crisis (because there is a conflict or contradiction between the two for whatever reason), your brain uses various self-defense mechanisms to justify your actions, way of life, and beliefs. People do not like finding out that they or their parents or something about how they have been operating their lives is contradictory/wrong/irrational.