shared_ptr

int main()
{
    //instruction 1 -> OK
    std::unique_ptr<int[]> sp2(new int[10]);

    //instruction 2 ->error does not compile
    std::shared_ptr<int[]> sp1(new int[10]);
}

I was reading about delete and delete[] when memory allocated for smart pointers is with new[]. Why instruction 1 with std::unique_ptr is ok and with std::shared_ptr isn't ?