Why is this random number generator generating same numbers?

The first one works, but the second one always returns the same value. Why would this happen and how am I supposed to fix this?

int main() {
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_real_distribution<> dis(0, 1);

    for(int i = 0; i < 10; i++) {

        std::cout << dis(gen) << std::endl;
    }return 0;
}

The one dosen't work:

double generateRandomNumber() {
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_real_distribution<> dis(0, 1);

    return dis(gen);
}



int main() {
    for(int i = 0; i < 10; i++) {
        std::cout << generateRandomNumber() << std::endl;
    }return 0;
}