Why setAccessible method can not change the constructor method to be accessible in php?

When I tried to use Reflection API to new instance of singleton pattern class in PHP, I failed, due to non-public construct function.

simple code:

<?php
class Singleton{
    private static $instance = null;

    protected function __construct(array $config = []){
        //do something...
    }

    public static function getInstance(array $config = []){
        $className = get_called_class();
        if (!isset(self::$instance[$className])){
            self::$instance[$className] = new static($config);
        }
        return self::$instance[$className];
    }
}

class likeDB extends Singleton{
    //...
}

function callbackRF($className, $methodName, array $args = [], array $params = []){
    //do something...

    $class = new ReflectionClass($className);

    //throw Exception
    $instance = $class->newInstanceArgs($args);

    //do something ...
}

And then, I tried to use $class->getConstructor()->setAccessible(true) before calling newInstanceArgs method. It also failed and the exception message was the same.

Now, I known these code could not get right instance of some class. But, I want to known why setAccessible method can not change the constructor method to be accessible ?