Why cannot we specify access modifiers inside an interface in C#?

Interface methods are contract with the outside world which specifies that class implementing this interface does a certain set of things.

Interface members are always public because the purpose of an interface is to enable other types to access a class or struct.

Interfaces can have access specifiers like protected or internal etc. Thus limiting 'the outside world' to a subset of 'the whole outside world'.

Example

interface IInterface{
   void Save();
}
class Program{
   static void Main(){
      Console.ReadLine();
   }
}

The above example will compile properly without any errors

Prior to C# 8, interface members were public by default. In fact, if you put an access modifier on an interface member (including public), it would generate a compiler error.

interface IInterface{
   Public void Save();
}
class Program{
   static void Main(){
      Console.ReadLine();
   }
}

The above code throws compile time error in c# 7.0,but in c# 8.0 it compiles without any error