C# vs Java - 为什么虚拟关键字是必要的？

我开始学习一些C#，我遇到了一个令人不安的问题：虚拟方法。这样的关键字是必要的吗？

Java中的简单多态性不需要虚拟关键字工作，甚至覆盖加注也是可选的：

package figures;

public class Figures {
    public static void main(String[] args) {
        Figure figure = new Figure();
        Circle circle = new Circle();
        Triangle triangle = new Triangle();
        Figure []arrayOfFigures = {figure, circle, triangle};
        for (int i = 0; i < 3; i++){
            arrayOfFigures[i].introduceYourself();
        }
    }
}

class Figure {
    public void introduceYourself(){
        System.out.println("I am just a figure.");
    }
}

class Circle extends Figure {
    @Override
    public void introduceYourself() {
        System.out.println("I am a circle.");
    }
}

class Triangle extends Figure {
    @Override
    public void introduceYourself() {
        System.out.println("I am a triangle.");
    }
}

而在 C# 中，相同的示例需要 virtual 和 override 关键字才能工作：

namespace Figures
{
    class Figures
    {
        static void Main(string[] args)
        {
            Figure figure = new Figure();
            Circle circle = new Circle();
            Triangle triangle = new Triangle();
            Figure[] arrayOfFigures = { figure, circle, triangle };
            for (int i = 0; i < 3; i++)
            {
                arrayOfFigures[i].IntroduceYourself();
            }
        }
    }
}

    class Figure
    {
        public virtual void IntroduceYourself()
        {
            System.Console.WriteLine("I am just a simple figure.");
        }
    }

    class Circle : Figure
    {
        public override void IntroduceYourself()
        {
            System.Console.WriteLine("I am a circle.");
        }
    }

    class Triangle : Figure
    {
        public override void IntroduceYourself()
        {
            System.Console.WriteLine("I am a triangle.");
        }
    }

通常有动机将一些关键字引入语言。由于C#是在Java和许多其他面向对象语言之后创建的，我想知道是否有理由引入强制性（多态性工作）和关键字？virtualoverride