why free() doesn't decrease programs data space

Question

My understanding is that malloc internally uses sbrk() and sbrk(0) gives pointer to current location of the program break. then according to following code :-

#include<stdio.h>
#include<malloc.h>
int main()
{
    printf("Before allocation :- %u\n",sbrk(0));

    int *ptr = malloc(sizeof(int)*100);
    printf("After Allocation of 400Bytes :- %u\n",sbrk(0));

    free(ptr);
    printf("After free() :- %u\n",sbrk(0));

    return 0;
}

output is :

Before allocation :- 37367808
After Allocation of 400Bytes :- 37502976
After free() :- 37502976

But after call of free() it should print again 37367808 instead it is printing 37502976.