Mathematical Reflection

@bingndensum Exactly.Music is a matter of consonant and dissonant ratios.The relationship of one note to another as defined by a strict mathematical ratio.The study of intervals as defined by the mathematical relationship of one note to another.The development of chord structure by the mathematical relationship of the notes within a chord to each other.Scales also follow and are defined by the mathematical relationship of one note to another.Rhythm and timing,tempo all mathematical.
If you want to understand music theory it is all a matter of ratios and their relationships to one another.Music without mathematics would only be noise.

Nature is working according to physical laws. If it didn't we wouldn't be here. Our solar system would not have formed if G in (G * m1 * m2) / r^2 could change its value from one second to another. *)

And having a physical law means being able to formulate it mathematically.

*) Yeah I know, this is Newton and thus not valid for very big masses and high velocities.

@Dukedog The Fibonacci sequence is everywhere too.

Because mathematical modelling of situations is convenient, simple, and matches with experiments.
Why? That's another question.

@Dukedog
If you want to know 'why' is maths everywhere then there's no reason since there are many things which are universal facts. If you want to know 'how' is maths everywhere, then let me tell you that it is involved in real life problems. It as applications in many fields some of which we might have never heard about!
For more, read: en.m.wikipedia.org/wiki/Areas_of_mathematics