Array loses value when returning PHP

Question

I have a function which reads CSV files of deleted orders.

I'm initiating an array at the top of the file, then array_pushing values into it but it loses value when the function ends.

My Code:

foreach($files as $file) {
    $order_numbers = [];

    $url = base_path('XML/verwijderde_orders/' . $file);

    Excel::load($url, function($reader) use ($order_numbers) {
        $results = $reader->get();
        foreach($results->all() as $row) {
            foreach($row->all() as $key => $value) {
                array_push($order_numbers, trim($value));
            }
        }
        dd($order_numbers); // has values here
        return $order_numbers;
    });

    dd($order_numbers); // has no value here


}

What am i doing wrong?

Any help is appreciated.