Laravel out of memory

Im trying to export my data to an excel sheet but I get the error:

FatalErrorException in Connection.php line 321: Allowed memory size of 134217728 bytes exhausted (tried to allocate 196605 bytes)

I understand I could just up the memory limit of php but I like to understand why my code takes up so much memory.

My code:

public function exportExcel()
{

    $datum = date("d-m-Y");


    Excel::create('Sales export '.$datum, function($excel) {


        $datum = date("d-m-Y");

        // Chain the setters
        $excel->setCreator('some name')
            ->setCompany('some company')
            ->setDescription('sales export.')
            ->setTitle('Salesexport '.$datum);

        $excel->sheet('sales '.$datum, function($sheet) {
            $orders = Order::orderBy('created_at','desc')->get();
            $sheet->appendRow(array(
                "merk","product","artikel nr","categorie","collectie","maat","omschrijving","inkoopprijs","verkoopprijs","prijs betaald","aantal verkocht","verkocht aan",  "totaal","dag","maand","jaar","kwartaal","reseller","verkoper","bestel naam"
            ));
            foreach($orders as $order)
            {

                foreach($order->products as $p)
                {

                    $sizeLink = $p->productSize;
                    $productLink = $sizeLink->product;


                    // Append row as very last
                    $sheet->appendRow(array(
                        //Merknaam  Artikelnr.  Soort   Kleur   Maat
                        //Omschrijving  Geboekt aantal  Basiseenheid
                        //inkoopprijs   verkoopprijs    aant stuks verkocht
                        //Maand Jaar    Kwartaal


                        $productLink->brand->name,
                        $productLink->name, 
                        $productLink->artnr, 
                        $productLink->category->name, 
                        $productLink->collection->name, 
                        $sizeLink->size->name,   
                        $productLink->desciption,   
                        number_format((float) $productLink->price_buy_in, 2, ',', ''), 
                        number_format((float) $productLink->price, 2, ',', ''), 
                        number_format((float) $p->price, 2, ',', ''), 
                        $p->quantity, //geboekt aantal
                        $order->billingname . $order->billingnamelast, 
                        number_format((float) $p->quantity * $p->price, 2, ',', ''), // totaal kosten
                        //number_format((float) ($p->quantity * $p->price - $p->quantity * $p->price_buy_in), 2, ',', ''), // winst inkoop-verkoop
                        date("d",strtotime($order->created_at)),
                        date("n",strtotime($order->created_at)), 
                        date("Y",strtotime($order->created_at)), 
                        ceil(date("m",strtotime($order->created_at))/3), 
                        $order->reseller->name,
                        $order->creator, 
                        $order->name, 
                    ));
                }
            }

            // Auto filter for entire sheet
            $sheet->setAutoFilter();
            $sheet->freezeFirstRow();
            // Set black background
            $sheet->row(1, function($row) {

                // call cell manipulation methods
                $row->setBackground('#cccccc');
                $row->setFontWeight("bold");

            });
    $sheet->setColumnFormat(array(
        'G' =>  \PHPExcel_Style_NumberFormat::FORMAT_NUMBER_00,
        'H' => '[$EUR ]#,##0.00_-',
        'I' =>  \PHPExcel_Style_NumberFormat::FORMAT_NUMBER_00,
    ));

        });

    })->download('xlsx');;
}

via Chebli Mohamed