Rrweriter function does not work at the beginning of the sentence

I have a rewriter function. I compare and replace the variables in the curly brackets with the ones in the text.

For example;

My variables are: [“Hello|Hi”,”How are you| What’s up”,”quick|rapid|swift|agile|brisk”]

Text: Hello, how are you?

Rewritten text: Hello, {How are you| what’s up}

Even if I add an extra word per sentence with str_replace, the first words do not change. Even if I change the first sentence to
“word_to_be_deleted Hello, how are you?” I still get the same result.

Sentences:

$sentences = ["Hello|Hi","How are you| What's up","quick|rapid|swift|agile|brisk"];

Rewrite function:

function rewriter($text) {
    global $sentences;
    $text = nl2br($text);
    $text = str_replace(', ', ' , ', $text);
    $text = str_replace(', ', ' , ', $text);
    $text = str_replace('?', ' ? ', $text);
    $text = str_replace('.', ' . ', $text);
    $text = str_replace('<br />', ' <br /> word_to_be_deleted ', $text);
    foreach ($sentences as $sentence) {
        $exsentence = explode('|', trim($sentence));
        $i = 0;
        foreach ($exsentence as $sax) {
            if (count($exsentence) > $i) {
                // $lastsentences[trim($exsentence[$i])] = implode('|', array_diff($exsentence, array($exsentence[$i])));
                $lastsentences[trim($exsentence[$i])] = implode('|', $exsentence);
            }
            $i++;
        }
    }
    // uzunluğa göre array'i diz
    array_multisort(array_map('strlen', array_keys($lastsentences)), SORT_DESC, $lastsentences);

    foreach ($lastsentences as $key => $value) {
        $text = preg_replace(sprintf('/{[^}]+}(*SKIP)(*F)|%s/i', preg_quote(' ' . $key . ' ', '/')), ' {<b style="color:red">' . $value . '</b>} ', ' ' . $text . ' ');
    }

    $text = str_replace(' | ', '|', $text);
    $text = str_replace(' , ', ', ', $text);
    $text = str_replace(' , ', ', ', $text);
    $text = str_replace('.  ', '. ', $text);
    $text = str_replace(' .', '.', $text);
    $text = str_replace(' .', '.', $text);
    $text = str_replace('word_to_be_deleted', '', $text);
    return html_entity_decode($text);
}

Headings that do not change even though the variable is defined: