Why can I use more array values ​than allocated when using realloc in C

Question

Test Case: I want to allocate memory using realloc() on an int array. I allocate memory for 2 values, but if I write the third value and so on to the array, they are also written and displayed. Why am I not getting a SegFault error?

P.s Exactly the same problem when using malloc()

#include <stdio.h>
#include <stdlib.h>

typedef struct Test
{
    int *nums;
} Test;

int main()
{
    Test test;

    test.nums = NULL;
    test.nums = realloc(test.nums, 2 * sizeof(int));

    test.nums[0] = 1;
    test.nums[1] = 2;
    test.nums[2] = 3;
    test.nums[3] = 4;
    test.nums[4] = 5;
        
    printf("%d %d %d %d %d\n", test.nums[0], test.nums[1], test.nums[2], test.nums[3], test.nums[4]);

    free(test.nums);

    return 0;
}