I suppose science never truly reaches the complete "why". Not yet, anyway.
For example, one could ask why adding vinegar to baking soda makes bubbles. Because it's an acid and base reaction and the transfer of hydrogen creates water and carbon dioxide. One can then ask why they react. In fact, one can keep asking why to each explanation until we need to get into the particle physics and eventually get to some property of matter that we don't truly understand and must explain with "because they just do."
In a sense, I think science is about trying to reduce the number of theories based on pure observations in an attempt to try to understand things from the 'core' properties. An analogy would be to be able to explain how a bit of code in a Java VM would work in terms of machine code.