Why does it take so many attempts to generate a random value between 1 and 10000?

I have the following code that generates an initial random number between 1 and 10000, then repeatedly generates a second random number until it matches the first:

let upper = 10000;
let randomNumber = getRandomNumber(upper);
let guess;
let attempt = 0;

function getRandomNumber(upper) {
  return Math.floor(Math.random() * upper) + 1;

}
while (guess !== randomNumber) {
  guess = getRandomNumber(upper);
  attempt += 1;

}
document.write('The randomNumber is ' + randomNumber);
document.write(' it took' + attempt);

I am confused at (attempt) variables. Why is it that the computer took this many attempts to get the randomNumber? Also, it didn't put attempt in the loop condition.