I don't believe that the answer to this is "because the task is difficult".
I actually think the answer is simply - because the life sciences are in their infancy. It's like asking a medieval astronomer why it's so difficult to fly to the moon.<p>At the end of the day we do science with our brains, and our brains are not built to understand biology. How could they be? To really be able to understand even the simplest, isolated biological process, you probably need to hold at least a thousand bits of data in working memory. You can build a model on a computer, but we still don't know what the important bits of data are out of many millions, we don't know when they are missing, and we don't know when our model begins to be valid and ceases to be valid.<p>In contrast, a physicist can gain deep insight about the ENTIRE universe while sitting under a tree with a pen and paper and some cogent abstractions. Furthermore, this insight is valid backwards and forwards in time except in clearly obvious extreme conditions.<p>This is actually completely amazing when you think about it. We would like to think the same about biology, and scientists act this way, but we would be mistaken. Abstractions fail in biology. Even the most basic and obvious abstractions made by humans, like the concept of a gene, are too simple to act as a foundation for ongoing discovery. And we don't have any alternative framework.