为什么泛型类型参数说"扩展"可比较而不是"实现"？

public class MyClass<T extends Comparable<T>> {
    public boolean compare(T t1, T t2) {
        return t1.compareTo(t2) == 0;
    }
}

public class MyString implements Comparable<String> {
    @Override
    public int compareTo(String o) {
        return 0;
    }
}

public class MyInteger implements Comparable<Integer> {
    @Override
    public int compareTo(Integer o) {
        return 0;
    }
}

MyClass<MyString> myStringClass = new MyClass<>();
MyClass<MyInteger> myIntegerClass = new MyClass<>();

myStringClass.compare(new MyString(), new MyString()); // 正常
myIntegerClass.compare(new MyInteger(), new MyInteger()); // 正常
myStringClass.compare(new MyString(), new MyInteger()); // 编译错误