Because physics is the only true science. Everything else is stamp collecting. [img]/images/graemlins/grin.gif[/img] (this was on the wall in my faculty at uni)

While mathematicians may be smart, they're little more than logicians. Physicists attempt to answer the broader questions of what actually exists and how and why it functions, whereas mathematicians focus on expressing the 'how' in logical terms. And developing methods for reducing the 'how' to something usable.

That's the pure side of it, in reality most mathematicians are smart logicians who crunch numbers and work on developing computer systems.