Plus: mathematicians really don't have spare time to learn every area that comes along. Allegedly Poincare was the last true polymath. Given how math has been developing for centuries and you never really need to throw things away it continually becomes harder to get up to speed in any particular field. There's a famous quote about how the Princeton undergraduate math program is so rigorous that it brings you up to speed, to the point of early twentieth century mathematics. In this way math is incomparable to CS.