The same reason why problems or research may relate to multiple fields within a given discipline.  Typically if there is a problem to be solved, somebody will find a way to use it.  I personally believe that a big part of what drives modern interdisciplinary research is the fact that computation plays a large role in preparing experiments and calculation.  The fact that a computer can perform calculations magnitudes faster than the scientist comes into play a lot.  Richard Hamming, a pioneer in computing when he was alive communicated these ideas a lot.  Once we actually had computers that could read programs that are implementations of algorithms presented by mathematicians/computer scientists, there was a need to study both formal and empirical together.  It is very common that formal sciences and empirical sciences are entwined because you can't say much about models with the theory behind them.  That's one reason why mathematicians/computer scientists/statisticians are invaluable when computation is involved and assisting in setting up a model.  If there was no communication between different fields, you'd find them discovering the same things over and over again.

The same reason why problems or research may relate to multiple fields within a given discipline.  Typically if there is a problem to be solved, somebody will find a way to use it.  I personally believe that a big part of what drives modern interdisciplinary research is the fact that computation plays a large role in preparing experiments and calculation.  The fact that a computer can perform calculations magnitudes faster than the scientist comes into play a lot.  Richard Hamming, a pioneer in computing when he was alive communicated these ideas a lot.  Once we actually had computers that could read programs that are implementations of algorithms presented by mathematicians/computer scientists, there was a need to study both formal and empirical together.  It is very common that formal sciences and empirical sciences are entwined because you can't say much about models with the theory behind them.  That's one reason why mathematicians/computer scientists/statisticians are invaluable when computation is involved and assisting in setting up a model.  If there was no communication between different fields, you'd find them discovering the same things over and over again.

@Daniel have given a good example of interdisciplinary  research regarding "mathematicians/computer scientists/statisticians" contribution to the research!

Furthermore, I would like to pay attention on fact that "Interdisciplinary research is starting to attract more and more attention — and funding..." Interdisciplinary research: Break out by Virginia Gewin is fine reading about the issue!

Researchers working at the interface of disciplines can pursue insights without sacrificing career progress.

http://www.nature.com/naturejobs/science/articles/10.1038/nj7509-371a

Much of research is funded by industry, without going into the drawbacks of that, the research requirement is for something useful in industry.

From an engineering perspective, there are few applications that will only cover a single discipline to arrive at something useful. e.g. an electric drive nowadays will cover power electronics, programming, mechanical engineering, Medium- and Low Voltage Power engineering etc.