Why aren't Array methods built into an Array instance?

Question

Sorry for what is probably a silly question but it's bugging me...

int[] i = {3, 2, 1};
//why
Array.Sort(i);
//instead of
i.Sort();

char c = 'c';
//why
char.IsLetter(c);
//instead of
c.Isletter();

Answer 1

Thanks to Pedro d'Aquino for identifying these other questions that provide answers.

The basic point is that instance methods on structures are not thread-safe but static methods are.

See these questions:

• Why is .NETs char.IsLower() a static method?
• Why IsNan() is a static method on the double class instead of an instance property?

Answer 2

These are utility methods that don't need to belong to these classes. This reinforces the Single Responsibility Principle

(edit) I was confusing with Java

(About static members):

Static class members can be used to separate data and behavior that is independent of any object identity: the data and functions do not change regardless of what happens to the object. Static classes can be used when there is no data or behavior in the class that depends on object identity.

The thread-safe point of view is also a good reason.