Why does my variable firstVowel not update in the following code?

Question

function pigLatin(word) {
  let finalWord = \'\'
  let vowels = [\'a\', \'e\', \'i\', \'o\', \'u\', \'A\', \'E\', \'I\', \'O\', \'U\'];
  let firstVowel = 0;
  if (v