You have $headers .= '...'; followed by $headers = '...';; the second line is overwriting the first.
Just put the $headers .= "Bcc: $emailList\r\n"; say after the Content-type line and it should be fine.
On a side note, the To is generally required; mail servers might mark your message as spam otherwise.
$headers = "From: [email protected]\r\n" .
"X-Mailer: php\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";
$headers .= "Bcc: $emailList\r\n";