Why Nobel prize is not given in maths?

Nobel prize is awarded for physics, chemistry, literature, peace, and physiology or medicine, but not for Maths. A lot of people wonder why there is no Nobel prize in this popular field, but the reason is still unclear.

One reason may be the Nobel's interests are practical sciences, as what he did in his life and in his opinion, Maths may be just the support tools for other sciences, not inventions or discoveries of greatest practical benefit to mankind.

Further, there existed already a well-known Scandinavian prize for mathematicians, Nobel probably didn't want his prize to be less competitive because of at that time Acta Mathematica (founded by Mittag-Leffler, one of the best mathematician at that time) was predominating in Maths.

Another rumor is that a woman Nobel proposed to his wife/his mistress rejected him because of a famous mathematician. But there is no historical evidence to support the story and Nobel was never married.