[Fester Chugabrew]

Because it is useful in mathematics. However, it doesn't exist in nature.

If you do not understand that abstract concepts are intertwined with nature, and that they are essential for collecting and sorting data, how are you ever going to make a good scientist?

[Junior]

Mathematically-abstract concepts can have concrete examples (pi, for instance). It is these that find use in science. Mathematically-abstract concepts that have no real-world counterpart (infinity, for example) are useless when it comes to scientific research.