When I generate random floats between -1 and 1, they are more often negative than positive. Why is that?

I am using glm::linearRand(-1.0f, 1.0f) to generate random floating point numbers between -1 and 1. Afterwards, I output the percentage of numbers that are positive (0.0f or above).

std::srand(time(0)); // Give glm a new seed

uint32_t samples = 1000000000;
uint32_t positive = 0;
uint32_t negative = 0;

for (uint32_t i = 0; i < samples; i++) {
    float rand = glm::linearRand(-1.0f, 1.0f);

    if (rand >= 0.0f) {
        positive++;
    } else {
        negative++;
    }
}

std::cout << "positive %: " << std::setprecision(6) << ((float)positive / samples) * 100 << std::endl;

The percentage of positive numbers always ends up around 49.6%, no matter how often I run the program (with different seeds!). If I understand floating point numbers correctly, there are equally many between -1.0f and 0.0f as there are between 0.0f and 1.0f.

So why does this program always generate more negative numbers than positive numbers?